To be honest GTA4 does not really not a very powerful gfx card.
Unfortunatly what is does need and what is non negotiable is.... 3 Cores.
Yes this is a hangover because thats the way the 360 version was obviously done and that was most liekyl their starting point for the port.
I doubt the game will ever be playable on a machine with less than three cores.
Without the 3 cores it is always barely playable regardless of the settings.
With 3 cores it runs nicely.
Unfortunatly this pretty much rules the game out on all macs!
Ahh well, I game on my PC. WOuld be nice to play is on my laptop too (a mac), but that will habve to wait for a future generation.
it is possible that with some optimisation things might run better on 2 cores but I think that would be too much ofa re-write to ever happen. Especially since the game is now out.
LOL, your hangover completely effected your grammar.

I on the other hand don't have an excuse -- well, I'm tired.
For the higher detail settings in GTAIV PC -- which a console can not handle, a more powerful GPU is needed. These mobile GPUs, especially the integrated GPUs still have bottlenecks compared to the desktop GPUs.
If the 360's proc wasn't rather week, you would have a point, but as is, it's a watered down Power PC. Each core only spits out 2 instructions and its VMX is a joke compared to modern SIMDS. All 3 cores combined are maybe on par with a single 1.8 Ghz G5 -- you can fill in the rest.
GTAIV was built on a console for its strengths, it was rushed to the PC.
When a port is done right for the PC, like Gears of War, Fallout 3, and Devil May Cry 4 to name a few, they not only look better than their console counterpart, but they run at higher frame-rates when played on "reasonable" PCs. Their minimum specs are also more realistic. I know RockStar can't perform magic, but I also know that if this game had been given more time, or had started out on the PC, they would have avoided many of these complaints and it would run better on more configurations.
Besides needing optimization, look at the 360 vs a PC and you'll see why so many PCs are having an issue. The difference is literally night and day with the PC version looking substantially better;
http://www.n4g.com/xbox360/News-249364.aspx