Don't expect to play many games with this setup. This video chip is nowhere near powerful enough to play much.
My advice is forget about overclocking (or try to get a stable 10% or so) and start trying game demos and see what you can play.
1) go to www.gamespot.com and find the PC section and show games by RATING (all games). Start going down the list for games made in 2000 or later. Google for demos and try them
2) get FRAPS to monitor your framerate. For high-end shooters you want at least 40FPS (60FPS is optimal for most flatscreens. 75 or 85 is usually optimal for CRT monitors).
You'd see a big performance with a dedicated graphics card but without knowing your other specs (CPU and RAM mainly) it's hard to recommend anything but if you had an okay dual-core I'd likely recommend something like the HD4770 but that's a very rough guess.