Scan for virus, assuming you have anti-virus installed. If you don't here's a free one
http://www.bitdefender.com/
Scan for spywareware and here's a free good one
http://www.superantispyware.com/
Update all driver, expecially the ones from Intel, make sure they are for Vista and the right version 32 or 64 Bit
Drivers should include motherboard chipset and video
http://downloadcenter.intel.com/default.aspx?iid=gg_work+home_dowloads
Update Network driver
Reboot computer when asked
Run atf-cleaner.exe
http://www.atribune.org/index.php?option=com_content&task=view&id=25&Itemid=25
Run ccleaner.exe
http://www.ccleaner.com/
Run defraggler.exe
http://www.defraggler.com/
Test your game again