A number of people have found that after installing OS X 10.6.7 the installation seems to have worked fine, but when they try opening and running iTunes they encounter problems with the program hanging. Sometimes the program hangs when the iTunes store is accessed, and sometimes when checking for updates, or at other times when the program is immediately opened.
People have tried tackling this issue by performing a permissions fix using Disk Utility, along with quitting and relaunching the program and reinstalling it. Despite these efforts the problem persists, but there are a couple of possible quick solutions:
A few people who have had problems with iTunes after updating the OS have found a quick restart of the system has cleared the issue. Try restarting the system and holding the Shift key to get into Safe Mode, which will clear some caches and perform some other maintenance tasks on the system. After this, restart the computer normally and try running iTunes again.
Remove iTunes preferences and cache
If a basic restart does not work, try resetting some of iTunes' preferences and other temporary items. Go to the /username/Library/Preferences/ folder and remove the file called com.apple.iTunes.plist (you may see a number of these that are 0KB in size and end with a seven-character string, so remove those as well). Then relaunch iTunes, and if the problem still persists, try removing the iTunes Store cache by going to the iTunes preferences, choosing Advanced, and clicking the button to reset the cache.