Peculiar because I believe that's a supported card. I would start by making sure you're using up to date drivers. Assuming you're playing other MMOs without any real issues. If the problem persists I'd definitely contact technical support (they'd have more information on potential problems related to hardware. For clarification I've placed the system requirements below.
OS: Windows XP(SP2)
CPU: Pentium 4 2.0 GHz
RAM: 2 GB
HDD: 5 GB Free
Graphics Card: GeForce 7600GT
Mind you all those are the minimum and the game actually runs very well on "lesser" hardware.
Note: When I was playing TERA Online I noticed my desktop (using a GeForce GTX 450 card) had some rendering problems on the editor while my notebook (running integrated Radeon HD 6520G graphics off of the CPU) didn't have this problem. Very strange indeed.