According to the front Malaysia's premier gaming mag PC Gamer, Grand Theft Auto IV is coming to the PC. Since I have no clue as to what is exactly coming with the package, it's time for gross speculation.
My guess is that it will just be a direct port of the Xbox 360 version, with the same stipulations that Rockstar has with Microsoft in tow. That means, probably, no downloadable content until the exclusive agreement ends with Microsoft. Regardless of content, I wonder if Rockstar will open up some development tools this time around? Grand Theft Auto: San Andreas has quite the community still surrounding it.