Flashing your GP32's firmware is basically a procedure to change the OPerating System of the unit to a different one. Windups is one of those replacements. So... instead of having the normal animated intro, then the Game.... MP3..... Link.... selectons, you get a sort of windows-type environment that can play mp3s, display text and a hgost of other things.
Flashing your firmware does hold some risk though, as if it goes wrong, you may not even be able to turn on your GP32....
Fresh batteries and reading the instructions for the flash is recommended....
Cheers