Your logic does not make sense at all.. a top of the line graphics card is bottlenecked by a 3-4 year old processor like a 800 DURON.... So a 9800 xt would barely work better than a geforce 4 on your computer... So you think you should spend 300-400 on a 256 meg 9800 xt? Yeah, maybe you need to stay in school a liiitle longer... a 800 duron was worthless when it came out.. let alone 3-4 years after it came out.. It is equivalent to a celeron...
To consider blowing 400 on one card rather than spend 600 to get a brand new entire rig barely half a year old technology wise is simply incredibly flawed logic... If you can't understand that, then you can simply join the millions of Americans in credit card debt(their logic is flawed and if you don't like the comparison, eh.. )