For anyone who uses Outlook Express and wants to keep all their messages, folders etc. intact, this is how I do it (and I have never lost a single message).
Create a new folder (I call mine "Email") preferably on your secondary hard drive, i.e. d:\Email
Open Outlook Express and go to:
Tools > Options > Maintenance
Click on the Store Folder button and change the default store folder to the folder you have just created. (In my case d:\email)
Now when I format my C: drive, and after reinstalling Windows, all I have to do is go back to my cleanly installed Outlook Express and change the Store Folder to d:\email and Hey Presto, my folders complete with all their messages reappear in Outlook Express and I can get on with using my email as if nothing had happened.
In any event, even if you only have one hard drive, it is worth while moving your email store to somewhere easier to find than c:\windows\applicationdata\blahblahblah - which is where Windows 98SE hides them (how about c:\my documents\email?) because it makes it much easier to make a backup.