[UPDATE: There's an alternative by using Alpha-To-Selection, which is fantastic, but I'm leaving the tut as-is since not all other image manipulation softwares have this function but have those similar items to follow along with the tut below, as tedious as it may be. I use Alpha-To-Selection 99% of the time now.]
If you don't have a pattern sample to use, you can always use a paper for a fill for an alpha or other shape. For this tutorial I'm using my Tabloid Alpha template and a paper from my kit Backpacks Forbidden. If you have the tabloid font you can copy, but any font will do.
You can always take your paper and turn it into a bucket fill, but the pattern file will be large and large file size tools tend to crash Gimp on even the best systems from time to time.
Open a file that's 3600 x 3600 pixels and transparent background at 300 dpi.
Have your text large enough to arrange nine at a time on a sheet like I did above. This allows you to embellish and be able to cut them apart using the guillotine tool without cutting into another alpha. Also, you want the alpha large enough to be high in quality (I have since increased the size of my alphas I create).
You can do one of two things to insert your paper. You can File>Open As Layer or you can open it as a separate image. To import it, in the paper's image menu select Edit>Copy. Then select your alpha image and Edit>Paste. Your layers dialog box will look like the image above. Click on the sheet icon marked with arrow #2. Your pasted layer was just added to a new layer.
Now click on the eye to hide the paper layer and select the alpha layer. Using the magic wand, click in the transparent areas on the image. Select the paper layer (still hidden) and Edit>Cut. You can check your work by clicking the eye to unhide the papers.
[Gimp Alternative: Click on the alpha layer, go to Layer>Alpha To Selection, then click on paper layer Select>Invert, Edit>Cut. You're done and can skip the steps below. Embellish your alphas with any shadows or bevels and save.]
If you were successful, you'll have an image similar to the one above. You may notice, as shown by the arrow, that the centers of some characters have not been cut. Not a problem. Keep repeating the steps above that you used to remove the centers.
On the alpha layer, click your wand in the center of your character, like above in the center of the number six. Then select your paper layer, Edit>Cut. Again, if you wish to check your work, unhide the paper layer.
Once you have deleted all of the unnecessary areas, you can embellish this further by adding a bevel, drop shadow, brush work, adding elements. In my case I chose to save as is and open it up in PSE6 and add a layer style. Since I don't like how PSE cuts apart alphas I'll open it back up in Gimp and use the guillotine tool to separate my alphas, create a preview, file in a folder, zip it up and upload it to 4shared to share with all of you.
The black alpha layer can be deleted or used. You can create a different looking drop shadow by using the blur tools, move tool and changing the opacity of the black layer.
I find the method I have used above, though a bit time consuming, gives a nicer edge on the alphas than had I chose to bucket fill. For some reason I find Gimp alters the edges a bit during a bucket fill. You can experiment with this and see for yourself. Vector shapes seem to avoid this problem. When I want to bucket fill a pattern, I'll just create a paper and use this method or I'll use the Script-Fu called Alpha to Logo>Glossy. Settings are to taste. For a flat effect (not layered alpha) I will uncheck the shadow and set all numbers to 0 or 1. Be sure the check the boxes for using a pattern instead of gradient.