iTunes 5.01 will not WORK!

I have donwloaded the new itunes 5.01 and well the probelm keeps hapening... everytime i download the new "better" program and then restart the computer with none of the antivirus activated. every single time i click on the itunes in the desktop or from the applications list the same window alert opens everysingle time and says "iTunes has encountered a problem and needs to close, sorry for the inconveinence"... i dont know what to do know i have read other peoples problems but nothing works