>Basically should I bother building it or should I just get a completed system?
depends on if you want to get your hands 'dirty'.
dell has specials they run from time to time...there was a recent one for a p4 533fsb system w/o monitor for ~$500.
amd systems aren't bad either. the big negative against them is that they run hot. but having a multi-fan unit underneath my desk buzzing away isn't exactly my idea of a ideal work environment...
also if you don't have a copy of xp, buying a prebuilt system system will take care of that as well.