My specs are:
Dell Optiplex 960 (it works on my Optiplex GX620)
3GB DDR2 RAM
ATI Radeon B276
Windows Vista Business
I have not touched the game (since the reinstall) except to launch LaunchGTAIV.exe or whatever it's called, the "Play GTA IV" (non-EFLC button), and the "Start" button (not the Windows start button, but the game that actually puts me in GTAIV).