BTW, if you want to check your hard drive, put it through some stress to see if it can finish.
Right-click on C: drive, select Properties, then Tools, and select the Check for Errors. I'm not sure about Vista or Windows 7, I still have XP, but this will initiate the CHKDSK the next time you restart your system, so this bypasses any system driver issues that may be causing the lockups (and also potential virus issues, unless you have a particularly nasty one).
If it is a failing hard drive you will likely start getting bad cluster error messages. The real test is whether or not your hard drive can finish the scan, if it doesn't and locks up you may want to start thinking about backing up your data. If it finishes fine, then its on to other issues.