A rumor circulating among French gaming journalists is that the PC version of GTA 4 will sometime next October.
The French journalists cite retail as the origin of the rumor/leak.
Traditionally, PC versions of GTA took six to eight months after their console counterparts to hit the market. Considering the recently announced GTA 4's console release date, this October release date is not that unusual.
Console version of GTA 4 was originally scheduled for an October, 2007 release before being delayed to April 29, 2008.