iTunes Library not valid??

When I try to open iTunes i get a message that says: " The file "iTunes Library" does not appear to be a valid iTunes library file. iTunes has created a new iTunes library and renamed this file to "iTunes Library (Damaged) 2".
It may say 2 because the same message came up this morning when I tried to open iTunes.
What I was doing when this happened: I had just downloaded a file from a music blog, I opened the folder, highlighted all the MP3's and then double clicked. Usually I have iTunes open when I do this. Then the above message box appeared.
I have a large iTunes music Library of about 5000 songs, approx 20GB. When I click on Finder and click on Music I see all my files along with 3 "iTunes Library (Damaged)" icons in a iTunes folder.
I use iTunes 7.6. I Have Tiger 10.4.11. I use an iBook 1.42Ghz with 1.5 GB Ram.
I want my music back, please help!
Thanx, Greg.