New computer

I've been asked to recommend a new pc that can be improved into a gaming pc. A freind has a son who is getting into gaming. He wants a decent PC that is not to expensive bit but can be built up by the son as the son gets $, or birthday gifts. I'm not into the cutting edge stuff. Suggestions? Should he spend on PCI express, or just AGP. What are the important things that should be in the base PC?

Thanks all,

The best current and future upgrade paths are all AMD64, but they might be a bit expensive.

Socket A is slowly being phased out, but it is still more than capable of running anything out there today at great
detail levels. Dont bother with more than 512Mb RAM for now, as that would be the 1st upgrade the son could buy himself. AGP Video Card, definitely. for PCI-E to be useful, the rest of the system would need to be very powerful and probably out of budget.