Single core and AGP, yep; time to start looking at a serious upgrade/overhaul.
SATA II, multi cores, intel's upcoming chipset and cpu of doom, PCI Express 2.0 DDR3....there are a TON of reasons why you should just rebuild from almost scratch. Tho if you're serious about it, I'd wait for intel's new chipset and the Nehalem, assuming you can hold out that long and can afford it.
Well, unless you're crazy like me and you're already eyeing the new
6 core xeon. ^^