I'm not too great with PC specs, and what is and isn't a great PC - personally I really don't care about that stuff, as long as I can get the job done. However, I've got a pentium 4 2.6ghz, with 512mb RAM and a GeForce MX 440 (I think thats it) graphics card, which is all over 3 years old and it runs Maya absolutely fine, no problems. I don't see whats wrong with your PC, but I would have thought you could buy a new graphics card and it should be fine for your needs. I hate the shops on Tottenham Cout road. The guy was probably just trying to get you to buy a whole new PC from him or something!
LisaG