what Temp is your computer inside.
Anyway, download Spyware doctor from download.com and then scan your pc remove all spyware, then simply download coolbits for O'c G'card. then goto your Display options once you have downloaded coolbits then Edit and O'c your Frequance, once done that, change your Ram from another another Slot, make sure its the 1st slot next to the CPU.
And your computer should not lag no longer.