Yeah, I would have to say that for the vast majority of dorm room residents and their guests, the three most important criteria are volume, volume, and volume. And if it is a lot of rap and hip-hop being played, then it is maximum bass volume (or perhaps vibration level), out of all proportion to the rest of the mix.
My recommendation is to find a local band, and invite them to practice in your room. That would be the ideal situation, for you and your neighbors.
Seriously, it is good advice to forget about surround, and just get a decent 2-ch. system, or perhaps 2.1. Even then you will have some speaker placement issues to deal with.
Monitor Audio makes a decent small system intended primarily for use with an iPod, but you could also drive it directly from your PC, using the mini-jack input. I think it is about $350, and even Stereophile liked it. It is not going to have great bass response, but will allow you to have a pretty musical system, and you can save your money for when you are in an apartment or house.