'restoring previous itunes library'

I can't find info on this ANYWHERE. I created a huge mess in itunes for nothing. One day i was fooling around with some duplicate software, and a few days later found itunes almost empty and completely panicked. Forgetting that i was fooling around with that software a few days prior, i think i missed out on the key 'show everything'. This is why I said i made the mess for nothing. I thought it to be odd that there was nothing in the trash. So, in a panick i just dragged the entire itunes music folder into itunes and the wheels started turning.
Now i have a huge mess I can't make sense of. Aside from the fact i seem to be missing 40gigs, there's duplicates galore- including duplicate podcasts. Some of the duplicates are different sizes??!! WTF
Any support i can find is restoring itunes from an ipod. I'm using itunes9 and have a folder 'previous itunes library'. Theres of course several files in it with different dates. I wanted to try restoring from my latest date but can't get anything to happen.
Any advice or links anyone might have?
Thanks all.