Hi,
I had a similar problem after having to re-install the OS from scratch. I saved ALL the outlook express files and restored them into the same directory and voila it was ok.
Of course, I was using prescisely the same version of outlook express as before so I dont know whether that'll be an issue for you.
Also I didn't have to integrate any new mail into the old - that made it easier.
Also... Initially I couldn't copy a couple of the files back. There was an error which I cant remember word for word now but was something like "not able to copy client registered files"
I was able to successfully copy them after a reboot but before starting, outlook express, though.
Hope that helps,
Cheers,
Tim.