[Electrum]

the last pre-built computer I bought ran Windows 3.1. I've built everything since then. Right now, it's hard to resist the attractive pricing on Dells, Gateways, etc. With the exception of the budget, bottom of the line units, the price is pretty comparable for what you get. The advantage of a build you own will be more apparent next year, when you want to upgrade something. Computer manufacturers have one objective, and that is make you buy another computer. To do this ,they severely limit the amount of ungradability their units have.
If you build your own, you can build for the future. For example, if you by a motherboard that can handle the latest, greatest generation of processors, even though you can put in a proccessor more reasonably priced, later, when pricing becomes attractive, a processor upgrade is possible, easy, and a lot cheaper than a whole new machine.
Another factor to consider is that many computer manufacturers are linking the software, including the OS to the hardware. If you decide to upgrade your motherboard, you may find that Windows will no longe work.