GTA IV Lag On Windows 7

My system has 2.6 GHz Dual Core Processor, 2GB RAM, and 9600GT 512MB graphic card and runs windows 7, i can play all games e.g crysis warhead, prototype etc, on max settings without any lag but when i run GTA IV it Lags and does not run very smoothly, i.e there are hiccups in between, What could be the culprit here, Is it windows 7?

Windows 7 is still not perfected. It could be the case, however GTA IV is known for being very badly ported to computer and needs a relies much more on the processor and needs a very fast processor.

Installing on XP right now and also read somewhere that if you disable windows event log in Win 7 the game will work fine, will try that after the installation is finished