It's not an update problem, it's the way the game is made.
GTA: IV is optimized for consoles like PS3 and Xbox 360, which have more CPU power than GPU power. In the PC version, Rockstar failed to redo the architecture of the game, so it still wants more CPU power than GPU power, making the game run slow. Most people don't have 3Ghz quad cores so it doesn't run very good and almost no computer can run it on high.
I myself have a AMD Athlon 64 X2 6000+ 3.0ghz Dual Core processor and an EVGA GeForce 9800GTX+ and it runs like crap on even the lowest settings. It runs about 20fps on lowest.
I would say the only solution is either buy a $300 quad core CPU or wait for a new patch that will hopefully shift some of the pressure onto the graphics card.