Hey Hag... check out this proggy:
http://www.repair-zip-files.com/
It is shareware, and only repairs zips less than 3MB if unregistered, but it wil still tell you if the archive is recoverable or not.
At least then you can see if the problem is fixable. If it is, i'm sure you could find a crack out there somewhere, but you didn't hear that from me :).