iTunes Help - New to Mac

Hi all... i have recently switched to Mac... i am having a peculiar problem with iTunes.. i am unable to quit from it. Every time i try quitting from iTunes, it starts up automatically ... i have no idea what is happening... its even not letting the system to shut down or restart or anything, the system message is coming like the application iTunes prevented the system from shutting down... I am running Leopard on Macbook (Black) 2.2GHz with 4GB RAM

Anybody has an idea, as to what might be the problem?????

 

Thanks a lot mkrishnan .. .. i had both installed.. now its ok. but it seems its quite a bug...