Here's what I'd get http://www.bodyguardz.com/BodyGuardz_for_Nintendo_DS_Lite_p/nl-bdsl-1106.htm. You won't have to worry about the screens or body a single bit. I've had one on my DS for almost a year. My brother got on for his iPhone and he loves it.
I'd check out http://www.bodyguardz.com/BodyGuardz_for_Microsoft_Zune_80GB_p/nl-bmz8-1207.htm they offer a full body skin so you don't have to use a bulky case.
I used to use a screen protector from http://www.screenguardz.com then I saw the full body skins here http://www.bodyguardz.com/BodyGuardz_for_Sony_PSP_2000_Series_PSP_Slim_p/nl-bsp2-0907.htm and absolutely love it.