i second that vote. anything you build is better than whatever Dell can offer you -- price wise, performance wise, stability, take your criteria Dell will lose.
the trouble is some people are really afraid of doing this. it has to do with the warranty for some people, i think. individual components have warranties on them, so you should feel confident with that. if you buy from a reputable vendor you can return faulty parts, if you get any (i thought i have faulty RAM one time, but I just had to use different DIMM slots -- then it was fine).
at work we have a contract with Dell (I absolutely hate this fact) and I was asked to price out 3 new comps, for myself, my boss and someone else. it ended up being like $1300 each and it was very basic really -- 820 CPU, 1GB DDR2-533, 160GB, 17" lcd, radeon x300 (default). it's just insane, i could build an AMD system for around $900 that would be as good or better.