Building your own PC is the cheapest option for a desktop, especially if you already have some hard drives, cd drives and RAM lying around. About 4 years ago I dropped $1100 on a shitty Compaq PC 'cuz I didn't know better. Within two years the CDRW drive, then the hard drive crapped out on me, so I built my own. Cannibalizing a stick of RAM, the Monitor, keyboard, mouse, and CDrom drive, I was able to build a set up equivalent to a computer being sold at the time for about $1400 for only $500. However, being a college student at the time I was able to buy Win XP Pro for only $35, if you're not a student XP home runs for about $90, and XP pro for ~$200.

Problem is that now I want a laptop 'cuz I've been hauling a desktop around to gigs and it's getting to be a pain in the ass. Can't build my own laptop, I refuse to buy from Dell/Compaq, so that leaves me looking at Apple. =P