I did it. Took a long time, which I'm not used to with a fast connection.
When I opened Outlook Express, they had installed a new version. Everything was gone, all emails, folders and address book.
System restore saved the day, then I went to the download site and read the fine print. Nope, they don't warn you, bastards.
Someone told me the files for OE could be searched for and backed up, but I couldn't find them.
btw- someone told me their daughter tried to do it to her laptop and got the blue screen of death. Ended up with a complete reinstall. Anecdotal, but who knows.