iTunes is one of the worst. Anything from Apple for Windows is bad. Think about it. Why would Apple do anything nice for Windows?
iTunes eats resources like a six year old would chew through a candy store. It will cause stutters in frame rates, impede network connections to the arenas, and cause rampant and errant disk activity which causes a host of other problems.
Running the Windows Aero desktop is also a resource problem.
If you have anything from Norton, McAfee, Intuit, Roxio, Apple, Adobe, and probably more, then you are sacrificing resources that should not be sacrificed.
NOTE: You can kill most of the Adobe things, but the others are married to the operating system once they are installed.