The site says they tested these four cards on two X48 based systems with Windows Vista x64 and ATI Catalyst 8.11 WHQL drivers and all they got was a crash right after the GTA4 welcome screen.
The site says NVIDIA cards also had some trouble, but after clicking the exe file several times the game would run fine. Hopefully AMD or Rockstar will quickly provide a solution for this problem.
It is of course possible that GTA 4 (PC) will run under different conditions (operating system, graphics card, driver, motherboard). But there are reports of users in our German forum and in the 3D Center forum that describe similar problems. It also seems like Nvidia cards are also negatively affected; we had to run the exe file several times before GTA 4 started.