Yeah, I agree with Haole.
Stop looking at big box store computers. Go to a place that custom builds PC's, so you can put the right hardware in there. You want something configurable and upgradable, not the throw-away stuff that you get from HP or Gateway.
Don't get me wrong: I use HP's, Dells, and Gateways on a daily basis. But I use them in a business environment. I wouldn't even consider buying one of those as my primary rig at home, since I want the flexibility of being able to upgrade whatever I want, whenever I want.
Consider this: I have 8 USB ports in use. I have 4 hard drives, 2 optical drives, a firewire card, and a PCMCIA/Cardbus reader. I've run through 4 motherboards, 6 video cards, more optical drives than I can count (I replace them once a year or so; the dust just kills em), and several sound cards. I would never have been able to do that with a "name brand" PC, but since I custom-built mine in an Antec Lanboy case, I can upgrade as I see fit.
Speaking of which, I think the Lanboy case is just about the best computer case ever made. It's aluminum, so it's light. It's got 2 huge fans, both of which feature rubber mounts, so they're quiet. It's also got snap-in hard drive trays with rubber grommets, also reducing the noise. It even comes wth a carry strap, so it's easy to take with me. It really is a great case for LAN parties or just to have if you find yourself moving it around frequently.