Switch to what? (Probably a dangerous question in the techie forum).

I'm on XP right now which I didn't think was that dated. I'm defragging because games became unplayable within an hour or so of playing, but I thought Vista was so power-hungry that with older processors (mine's 2Ghz) it slowed down games too much anyway..?

The hard drive is quite old, maybe 7 years or so.

Oh, and defrag stopped at 25% or so because it couldn't defrag all files for some reason. Cure?