The main thing is 32 bit or 64 bit is not a problem for gaming in olden days upto 2010. beside that gta4 released in the end of 2008.
firstly, GTA 4 require best configuration to run smoothly. potato PC wont support GTA 4 , Even if potato pc supports GTA 4 there will be mind blowing Lagging that every gamer hates..
Atleast there should be Nvidia gt 730 or above and 4 gigs of ram to run GTA4 smoothly on either 32 bit or 64 bit
conclusion: 32 bit or 64 bit is not matter the main thing is you Should have good hardware configuration.