Welcome aboard.
Tweaking is more likely to get rid of visual glitches then improve performance. For better performance, overclocking is gonna yield more results, but that isn't gonna help getting a 7300 moving. It's pretty low spec. For some decent performance I'd look to a 7600/8600/9600 or better, or an ATI equivalent.
For the moment, you could try turning of graphic options in-game and playing at low res, but a graphics upgrade is gonna be desirable.
Hope it helps.
