I would try 1 or 2 things before a HDD wipe. If you have a fresh OS, chances are things will run a lot smoother. The underlying issue might be caused by something completely different, however.
1st, run Mafia 2 or another game that you've been having problems with. On the keyboard, press ctrl+alt+delete. Now, at the top, click the 'performance' tab, and see how your physical memory usage is. You didn't list your system specs, and you mentioned 1gb of RAM, which I'm assuming is the size of your video memory. Nonetheless, it wouldn't hurt to check to see just how many resources are being used up by these games.
2nd, download a temperature monitor online. I know of 2 right off the top of my head. There's hardware monitor, from the same developers as cpuid: CPUID - System & hardware benchmark, monitoring, reporting
There's also realtemp: Real Temp - CPU temperature monitoring
Once you've downloaded either one, install and run it. Jot down the temps that it reads and report back with your findings.