Theme Generator can make the .tsk file for you. I took a picture of my gf roughly 800x600 and Theme Generator helps you crop out what you want, and also focus in on what you want to show on your handheld.
use photoshop or alike to reduce size down to 240x268, save as jpg, then copy into your axim. open it in "my picture", then set it as you today wallpaper (select crop to fit). have fun!
here you go nyfreakll. MS has a theme generator for PPC. you can select the image you want and then use the theme generator to automatically size the picture and crop just what you want to use.
I've used that program to make the .tsk files and it worked perfectly in WM2003. I don't use it to sync the themes up though, I think that's the only aspect exclusive to PPC2002.
Just to recap what I did. I made the .tsk file using that program and I just dragged and dropped it to "My Documents" on my handheld. When I went into the Today settings on my x3i it recognized it as a theme file right away.