it's because of the wallpaper scrolling trough screens (so you need a wider wallpaper) and because toshiba can't do anything right (software wise).
the best solution, in my opinion. is to find/make a picture that's 1024*600. make a canvas around it in photoshop: like here
save as a .png and put it into /toshiba/wallpaper/ using rootexplorer.
then (in launcherpro) disable wallpaper scrolling.
then you can select it from the toshiba gallery, and it won't be cropped.
someone should really make an app doing this automatically. i'm unfortunately no developer, so i have no idea.
HTC Desire HD @ CyanogenMod 7
Samsung Galaxy 5 @ Motafoca 2.0.8b
Toshiba Folio 100 @ Foliomod 1.4