I ar lagggggggin!:(

[Danny]

OK. I hope this helps ;P took me 20 min x)

Sorry, but it probably wont help.
Judging by specs that you'd posted before, it's obviously not a hardware problem.
Have you tried scanning for viruses? That seems like the most likely scenario.
Ultimately you could re-install GTA to see if it still lags.

Before that, you might want to try installing Ccleaner to clean up your registry, and delete your temp files. (type %temp% in "Run", all the files in the folder that opens can be deleted)