How Come When I Start Using iTunes

(please don't bump w/o new info)

Avg temp should be easy to find with a little googling.
iTunes is a bit of a resource hog, so while I can't say much about the temp jump, it definitely uses more processor which means more heat generated.

Do you have an especially huge iTunes library, or some plug-ins, or are you using coverflow, or the "visualizer"?

 

iTunes must be doing something CPU intensive. Try clicking the little arrow in the monochromatic display in the top part of the iTunes window to cycle through the tasks that iTunes is doing.

 

Are you using the visualizer? Do you have "sound enhancer" on? (preferences->playback->uncheck Sound Enhancer to disable it) Both of these will use extra CPU time.