Sorry, just to add something helpful to my rant - motherboard with lots of firewire ports and USB ports, as much of the fastest ram as you can afford, the fastest processor you can afford and a decent hard drive with a reasonable amount of space. Don't go overboard on the internal HD, much better to get a series of external HDs than one massive internal. The more externals you have, the more inclined you will be to backup your projects, and store things in seperate paces. Data stored in seperate places is safer than everything stored in one place.

Would recommend having a decent core harddrive, then just run firewire externals. Think everyone should get out of the habit of relying on internal HDs. You basically want a core shell of a PC that runs quick and beefy, and gives you options to connect external firewire HDs, soundcards etc etc.