Got a HD 5970 and i found this site if your having troubles with flickering then this did the trick for me and this is what he put

Seems the problem may not be with ATI or Nvidia drivers but with the Crysis 2 ver 1.1 auto update. Open Crysis 2 root file, open backup folder copy Crysis2.exe.bak and rename as Crysis2.exe. Open Bin32 folder (if you are using 64bit OS) and Replace Crysis2.exe file with the one you have just renamed from the backup folder. Seems it works perfectly - running at 90fps no flickering!! Hope it helps you all"

do as above and off you go