I would not spend $2400 on a computer unless you are doing something cutting-edge with it (video editing, 3d modeling etc). Instead my advice is this: Buy a good desktop system for say $1200, put the other half in the bank. When your computer becomes too old, you already have money (more than enough) to replace it.
A desktop will provide you with more value than a laptop, better reliability, and upgradability for the same money. If you are concerned about space, get an LCD monitor, and maybe a wireless mouse and KB. Then it won't really take up more space than a laptop.
As far as brands go, I personally don't like Dell anymore and I would steer clear from them, although they do have some nice displays. I have heard a lot of good things about
http://www.ibuypower.com/mall/lobby.htm and you can get a pretty damn beefcake computer from them for $1200. I think Alienware's are pretty decent, although on the overpriced side.
Apple's are great and an Imac G5 would be plenty powerfull and fauirly good if you are concerned about space. You don't have to worry about Virii, Spyware and a host of windows problems. Some people will say "you can't get any software for them" but basically all of the popular stuff out there is for mac as well, except for some games.
HTH,
Pete
