Without providing details on exactly what you did it is hard to provide an answer. It's like me saying, "This chocolate cake I made tastes wrong," but not providing the recipe for review. Maybe it was the garlic in that particular recipe.
If iTunes is successfully using a previous library which you rename to iTunes Library.itl then that is now the current library.
Have you restarted your computer and then tried emptying the trash?
Limnos is correct. If it's working it's working. If you have a large number of 'previous libraries', Apple says you can delete them. Just keep the latest two or three. Or, no big deal if you keep them all.
Anytime you can't empty the trash because an item is "in use", and you're sure it's not, restart.
Thanks Limnos! Although I used no garlic, I understand the lack of specifics made a clearer diagnostic erm.. difficult. I'm still getting a couple of weird error messages upon startup, but I can deal with those much better than I could with iTunes 11!
Restart worked like a charm as well. I had tried renaming my iTunes library before, but I had tried to rename the wrong one. (not enough coffee today, methinks.) Anywho, thanks much for the help!