personal opinion, go for a DS hands down. i traded in my PSP towards my xbox 360 (paid off almost half of it so yea). as for RPGs they made Lunar: Dragon Song for the DS, but yea you don't want that

as much as i love the lunar games, that one blows. go for mainly the GBA games... fire emblem (although i think they play really slow..), the final fantasy games (final fantasy IV is coming out in december i believe), riviera (if you can find it) and there's a lot of others... for the PSP theyre making a few, but all remakes.
however, the DS does have a lot of really great games that have just / are coming out real soon. advanced wars: dual strike is an excellent game. i absolutely LOVE it. the new castlevania was awesome, mario kart just came out and that's a ton of fun, animal crossing is coming out on december 5th (somewhere around there) and that game was really addictive for the gamecube, warioware, super mario 64 remake, etc etc. there's a lot of great games for the DS, whereas all i liked personally for the PSP was lumines (which was awesome), and hot shots golf (which got kinda boring after a while). i heard GTA was good, but i'm not really into those games that much.
as for the whole music and movies thing, it's kinda cool, but IMO it gets real old real fast. as for the buying DVD's for it think about it this way... DVDs on the PSP cost normally $25 (some are 20 at release, but not many). so you could either buy it for $25 for the PSP or you could buy it for $20 at <insert nearest retail store here>, AND get special features with the regular DVD. so yea i would rather spend a bit less and get special features as an option. i won't even mention that normally a PSP will only last for about 1.5 movies on average for battery life.
i work as a manager at gamestop irl so i hear alot about this stuff. just to let you know if you plan on getting a PSP it's gonna cost you a lot more than a DS... if you wanna do the whole music / movie thing you gotta spend another at least $50 or more to get a big enough memory card for it. hope i helped
