Personally, I'd never go back to buying computers from the mainline companies. All the bulkware they load on combined with sub-par hardware will slow you down a lot.
A few years ago, I bought a computer (HP or compaq or something, can't remember) 3.0 gHz 1 gig ram blah blah. It just wasn't running that fast. There always was a pause before it would respond to commands, like right-clicking the desktop. I ended up formatting and reinstalling windows and it ran about twice as fast as before - but still not so great. Fortunately, the monitor went out while I was still under warranty at the store, so I took it back.
Ended up putting together and ordering a custom rig (from cyberpowersystem.com I think) with the same exact specs as the other comp, except they just load windows and office if you order it, and you get better quality hardware. It was lightyears ahead of the store-bought computer in speed.
Anyway, I'd recommend looking at getting a laptop from abs (www.abs.com) or cyber power (www.cyberpowerpc.com) or something. Anyway, just my 2c.