I love using the look of vellum in my digi-scrapping pages. Maybe it's because I was a paper scrapper for so long and I used vellum all the time for journaling -- hand written or with fonts. In paper scrapping, using vellum is an easy way to not have to plan ahead for where you're going to journal, and it's an easy way to get around needing journaling to show up on a dark or patterned piece of paper. (Here's a paper page of my dad and my son.)
So where do you get digital vellum? You make it yourself -- all you need is a white canvas/document/workspace (whatever you want to call it), the Marquee Tool, the Move Tool, and the opacity slider in the Layers Palette.
Ok, so first create your layout and leave a general area open that you're going to use the vellum in. Once you're ready for that part, choose the Marquee Tool (Make sure it's the Rectangular one, rather than the Elliptical.) Make a selection that outlines exactly where you'll want the vellum layer. (This CAN be a rough estimate -- you'll have a chance to adjust it later.) This selection will stay active until you deselect it. We'll use it in a minute. (Here is a page I was working on of my good friend's twins. This has the text already there, but it seems to be missing something.)
Now you need to open a new, blank document. Hold down the "ctrl" and "N" keys (this is the same as "File > New.") In the window that pops up, under "preset sizes," select one that is similar to your layout size (I often choose "8x10") and under "contents" make sure the bullet next to "white" is selected. Then hit "ok." This will give you a new, white document. (Here is what the selection in the layout and then the opened white document look like.)
Click on the blue title bar of your layout to make that window active again. (If you click IN your layout to make it active, the selection might deselect if you click more than once. If this happens, just go to "Edit > Undo Deselect.") The Marquee Tool should still be your active tool. Click and hold within the selection you made (you know, inside the rectangle with the dancing ants) and drag that rectangle over to your blank white document. (You'll just be dragging the selection outline.) Once it's there, click inside and drag it around to make sure the entire selection is on the canvas if needed. Then go to the Tool Box and choose the "Move Tool." Click within the selection in your white document and drag over to your layout -- this time you'll be dragging a white rectangle. After the white rectangle shows up in your layout, you can close your blank white document. (Shown here is what the selection looks like on the white document.)
Position the white rectangle where you want your vellum to be. You can use the Rectangular Marquee Tool to trim this rectangle if needed -- or you can use the Move Tool and bounding box to enlarge the rectangle and THEN trim it (you can do this at any time -- since it's just a white layer, you can enlarge it as much as you need to and not worry about losing "quality.") With the white rectangle layer selected, go to your layers palette. See the image at the right for the location of the opacity slider (top right of the palette.) Click on the blue arrow to open the slider, and watch the white rectangle to see how it changes as you move the slider. Choose the Opacity that will look best for your layout. Once you have it where you want it, just click anywhere outside the slider to "set" it and move on with working. You can always change the opacity percentage later. I usually use anywhere from 40% to 80%, depending on how dark the paper underneath the vellum is (or how busy the pattern is!) (Here is how that page of the twins turned out.)
Now you can add your text over the vellum and make adjustments accordingly. The goal here is to make your text easily readable, while still maintaining some sense of the paper underneath.
I usually "anchor" my vellum in some way (so it doesn't look like it's just randomly there.) I like to use either brads in each corner (seriously . . . can you tell I'm still majorly a paper scrapper?!) or stitching.
The brads are way easy. Well, if you have a Photoshop version that supports guide lines. With the Move Tool selected and the rulers showing (don't know how to do this? Read "Rulers, Guides, and Grids"), click and drag from inside the ruler onto your layout. This will make a new guide (a blue line.) Drag it to just inside one side of your vellum. Then do this 3 more times so all sides of your vellum have a blue line just inside of them, about the same distance from the outside. (See image below, at right.) Where the guide lines intersect is where you'll position the brads. If you want to use the same brad for each corner, just open it and drag the brad over to your layout, ONCE. I think it's easier to select that layer and in the Layers Pallette, right click and choose "duplicate layer" rather than dragging four over. (Plus, they'll have similar names for easy finding in the Layers Pallette -- it will be like "Layer 12," Layer 12 Copy," Layer 12 Copy 2," etc.) The new duplicate layer will be right on top of the original, but it will be the selected/active layer -- so you'll just have to drag it away to where it goes. If you're using different colored brads, then open and drag them all over and place them. After they're placed, you can drag the guide lines back to the rulers to make them disappear. (You can only make adjustments to the guide lines if you have the Move Tool selected.)
Now for stitching. This is sometimes more complicated, especially if you're working with a canvas smaller than 12x12 (I work with 8.5x11 and 8x8. Stitch files are usually 12 inches or more.) Most likely the stitching will be too big (both too long, and it will LOOK too big) and you'll have to make adjustments. I think it's easier to make adjustments AFTER you've drug it to your layout. Just drag ONE stitching line to your layout, even though you'll be using several. Work with the longest length of your vellum so you only have to fine-tune the size once (and then can use "duplicate layer" for the other stitches you need.) You can either use the bounding box to resize through the Move Tool, or you can click once on the bounding box to open up the Tool Options bar, and play with the percentages of height and width. (That is explained in The Move Tool basics) Don't be afraid to delete parts of the stitching layer that are too long.
Once you have your first stitching layer just right and placed where you want it, what do you do if you want to put stitching on all four sides of your vellum? Easy. Make sure the stitching layer is active, then in the Layers Pallette, right click and "duplicate layer." For the first one, drag it over to the matching side of the vellum. Duplicate the layer again. The new layer will be active -- click once on one of the bounding boxes, and in the Tool Options Bar, find the box that lets you rotate by percentage. (See image below this paragraph.) Type in "90" and a horizontal line is suddenly a vertical line. Place this line and trim it if needed, then copy this layer for the final side. If you have trouble "selecting" the stitching because it's so small, try selecting the layer from the Layers Pallette, and then with its bounding box showing it will be easier to move. OR, hit the "Z" key to select the Zoom Tool, then zoom in on the element you need to work with. When you're looking at it way close up, it will be much easier to maneuver.
Have fun! For a fun variation, try making vellum with other colors (using the Eye Dropper) or using patterned paper. One more tip: using the Opacity Slider on a piece of patterned paper with a black or white layer underneath is a great way to darken or brighten the patterned paper.