Depends on which version of iMovie. For iMovie11(v9) you should have an iMovie Projects Folder in your HomeFolder>Movies Folder. Your Projects are in there.
For the current iMovie10, they'll be in the iMovie Library folder, which should also be in your Movies Folder.
The preferences for both are in Home Folder>Library>Preferences, but as neither version of iMovie have much in the way of preferences, I shouldn't worry too much about them.