GTA IV: Unofficial patch for the 512 MB limit in graphic settings.
Rockstar recently released a new patch for GTA IV in which they completely removed the online game mode along with many commandline.txt functions that could be used to increase the game's memory limit. One such feature they removed was the resource usage limit feature. Therefore, currently, most users of AMD video cards are limited to only 512 megabytes of video memory.
This small patch removes the 512MB video memory limit, allowing your video card to work at its full potential!