Although you state that the reasons are too long to go into, I think you should investigate why you can't get into your account with that ID. It is simply an ID (identifier), so even if you no longer use your AOL account, you should be able to get into your Apple account using the same set of letters as your ID.
Note the difference between AOL account and Apple account. They're two separate accounts, both using the same text to identify your account, but with different passwords. Perhaps that's the issue, did you use the password for AOL when trying to sign into your Apple account? I recall having to get my head around the fact that Apple insisted on users using their email address as their Apple username. I thought at the time that it would lead to confusion.
I assume that once you get into your Apple account, you should be able to go to your account settings and update the email address.
By the way, to expand on what ed2345 mentioned, if you do create a new user ID, you will not get access via account that to any music purchased from the iTunes Store using your previous account. But as ed stated, this does not affect music ripped from your CDs or purchased from other online stores.
