Hmm, the .esi file itself is no problem - as Qwill already suggested, it is really just a .zip of your library files. If you take your copy to the PC and rename it to "xxxx.zip", you can easily access all your files again.
This way you can at least easily regain your pdfs, pictures, books etc. You can even get to your journals etc. and using the EdgeSync tool you can at least read them on your PC. However, as of yet, I am not able to get esi files back into the edge - the point is not so much that the mac address would be encoded in the file, but that entourage registers all library entries in a database which I haven't quite "hacked" yet. Why the guys from Entourage should not be able to port esis between different edges, though? Beats me!