|Are you sure you want to invest in that system? The CPU is outdated, the board only supports up to 2GB RAM (not nearly enough for Vista or Win7), the onboard graphics sucks, & the power supply is weak.|
At the very least, you need to max the RAM aount, & add a low end gaming card such as the ones listed by toxict51. If you want to run a higher end graphics card, you will have to upgrade the power supply. But there's no point into going too high end with the card though because it will be bottlenecked by the crappy Pentium D.