Have you downloaded and installed Windows Vista Service Pack 1 yet?
This may assist you with that you are running into. If you have already done this let me know. Could still potentially be something going on with the Apple Software.
If this is the case the link below describes how to fully clean out Apple Software. Possible file that belongs to Apple may of become corrupted and thus causing iTunes not to launch Properly.
But before you check the article out. Have you right clicked on the iTunes Application and chose Run as Administrator?
You can also right click on the iTunes App, Select Properties, and select Compatibility Mode - And make sure that is not turned on and set for something else. As this could potentially be running in a different mode.
http://support.apple.com/kb/HT1926?viewlocale=en_US