To get your Bookpedia over from one computer to the next, the most important part is the Bookpedia data folder. By default this is located in your Home folder under ~/Library/Application Support/Bookpedia. Create a copy of that folder and move it to your new computer or burn it onto a DVD. (Please note that there are two Application Support folders on your computer, one in the Home folder and one on your HD. You want the one in your Home folder.)
Once that's copied over/burned, you can also make a copy of the Bookpedia plist file so you won't have to re-register the program and keep other preference settings in the program as well. You'll find it in your Home folder under ~/Library/Preferences/com.bruji.bookpedia.plist
If you're on Lion, it hides the Library folder by default but you can use the Finder's 'Go' menu, hold down the Option key and the Library folder will appear.
Make sure you move the folder and the plist file into the exact same location on your new hard drive while Bookpedia is NOT running. Once they're in place, run the program and you'll see your database as before.