Here is what I did to one of my old keyboards to make it Dvorak. It might be a good idea to try it on an old keyboard first to get a hang of the process.
1. Use a photo manipulation program to make new key tops with the numbers.
2. Print them on either photo paper or plastic film.
3. cut to size of keytops (slightly smaller might last longer)
4. Coat tops of keys with a thin layer of 5 minute epoxy, applying decals as you go.
5. Apply a small dab of epoxy on top of each decal.
6. Put wax paper on top of the epoxy, press until smooth.
7. Let epoxy dry, remove wax paper.
8. Use an emory board to remove any excess epoxy.
If you want a slightly more dull look, try some extremely fine grit sandpaper.
There you go! If you do it right, it should look like the keyboaard was supposed to be that way, and it will last quite a long time.