PopinFresh, I feel your pain! I have exactly the same situation. Registered an old hotmail address with my itunes account back in 2004, used it to purchase a stack of music and apps, (Including TomTom). 2 years ago, I signed up for MobileMe and gained a new me.com email address. I have since used it to make further purchases of both apps and music.
Now I am stuck in the same double account nightmare and so many others are. This situations is particularly annoying on the iphone, when app updates appear, I have to sign out of one account and into the other to update, really annoying!
Based on Apple's normally intuitive "It just works" mentality, I thought they'd be a simple way to merge the 2 accounts and move all my purchases to my me.com account, but sadly after much forum searching it appears no-one has had much luck.
This situation is even more pressing with the expected arrival of iCloud and the auto updates on the iphone. I really don't want to have 2 accounts any more!
Apple please come up with a solution to merge 2 itunes accounts...