The first thing I'd try is Disk Warrior. The desktop directory might be corrupt, which is what is keeping FileMaker from opening the document. If that doesn't work, then I'd give Norton Utilities a try. It's still pretty good at file recovery and restoration.
Failing that, you could try TechTools but I've seen few situations where it did anything helpful that Disk Warrior didn't do.
i was using file maker pro on a powerbook, and it unexpectedly closed. when i tried to open it, it gave me that little watch thing and wouldnt open. so i restarted, and now its telling me that the file is damaged and i need to recover it. how would i go about recovering it?