Well, then, First of all, OC that C2D.
Core2Duo Overclocking Guide v1.1
Use MSCONFIG and google to decrease running processes.
Set RAM Timmings to 4-4-4-12 is not already at that. (Follow the Guide linked)
Set Page file to static and make 1024 MB. (in system, performence, oh you have vista, have fun looking for pagefile)
Defrag your Drive using O&O or Disk Keeper.
Doing all that should increase performence.