I'm going to recommend Dell as well. Although I build my personal machines, we use Dell workstations at work almost exclusively. We started leasing them just over a year ago and the majority of the company now has them. In that timespan we have had MINIMAL hardware problems.
Because of the good experience at work, I had my folks buy my sister a Dell for school. Looking at this home oriented machine, it appears to be just as solid as the business workstations, though it needs a memory upgrade badly (only 128). The only real downfall as others have mentioned is uninstalling all the 'free' stuff they give you. But thats going to be with any pre-built system.
I'm really rambling here so I'll finish up, I'd say go for Dell, but if you choose to build your own machine, there are plenty of us (me included) in the area that do computer support or admin for a living and could help you out if needed. Happy shopping!
EDIT: Keep in mind your gonna be charged upwards of 100 bucks for shipping these things, probably something to keep in mind when price searching the mail order companies.
