After reading this thread, I began looking around the web, and here is what I found.
Like Moose said, toothpaste is supposed to work well on all PDA's.
The whitening toothpaste works really well on deep scratches, as it buffers the screen down.
3M Professional Plastic Cleaner is supposed to work good also. You can find this product here.
This stuff is like what Dan was talking about, and looks like it would work.
I personally have not tried any of these scratch removers, so use at your own risk.
