When I have had to transfer my iPhoto library, I would just burn all my pictures folders on to a DVD-RW in iPhoto.
Then when I insert the DVD, I can just drag all the folders from the DVD to my library in iPhoto.
Obviouslly, this isn't too helpful if you dont have a DVD burner. But, if your iPhoto library isn't too big, you could use the same method, but just use a couple CD-RWs.