Linux Mint may be based on Ubuntu 9.04, but it's
not Ubuntu 9.04. I don't know what the makers of Linux Mint have done regarding the packages that are present, but there's obviously something extra they've done. You can't blame Ubuntu for this.
All I can tell you is that the maker of aTunes is NOT packaging up his .DEB file correctly, because -- and this is just my own experience, YMMV -- in my four years now of working with Ubuntu, I've
never had package dependency problems unless I was trying to install something that wasn't meant for the version of Ubuntu I was using at the time.
All I can tell you is to try posting a message on aTunes' message board (I'm sure they've got some kind of bug reporter), but don't worry -- the problem isn't caused by either you or Ubuntu, you're blameless.
You're not!
However, just like when you install an unsupported app on a Blackberry or Windows Mobile (or crack your iPhone), it's up to
you to fix your own problems by that point.
This is why the founder of Ubuntu (Mark Shuttleworth) keeps banging his head against the wall because people don't seem to understand that Ubuntu *is not a replacement for Windows* -- the practices and behaviors you're used to with Windows aren't going to be the same. You get pre-installed apps that do
almost everything you need with Ubuntu (like, instead of trying to install a music manager like you are, try using the pre-installed Rhythmbox application) -- there's no need to get frustrated over installing things you find on the internet.