Your safest bet is to move the OE Mail Store to a new folder, on a different partition, if available and export a few Registry keys to back up all your settings.

1. In Outlook Express, go to Tools - Options - Maintenance.
   
   Select the Store Folder button.
   
   Change the location of the Outlook Express Mail and News store folder to a drive/partition/folder that will not be affected by the uninstall or re-install.
   
   This is especially true if you plan to reformat the system drive. You will be prompted to log off/back on, or reboot, do so.
   
   
2. Do a Find on *.wab and copy all WAB files to a folder on the same drive/partition you used in Step 1. This can even be the same folder that you moved the Mail Store to (recommended).
   
   
3. Open Regedit and go to HKEY_CURRENT_USER\Software\Microsoft\WAB\WAB4\Wab File Name. Modify the value to point to the folder you copied your WAB file to.
   
   NOTE: If you only have one available partition, complete steps 1 through 3. Then backup the contents of the folder(s) that you moved the Mail Store and WAB files to. This can be to floppy media, CR-R/RW or whatever you prefer.
   
   
4. Now export the following 4 Registry keys to a location that will be available after your reinstall, or whatever (a floppy will work for the REG files). If you're going back to a Windows 9X OS, you need to ensure you select Win9x/NT4 in the Save as type pull down.
   

   HKEY_CURRENT_USER\Identities
   HKEY_CURRENT_USER\Software\Microsoft\Internet Account Manager
   HKEY_CURRENT_USER\Software\Microsoft\Outlook Express
   HKEY_CURRENT_USER\Software\Microsoft\WAB\WAB4\Wab File Name

   
   
5. Uninstall XP and/or reinstall your desired OS.
   
   NOTE: DO NOT open Outlook Express until you completed this procedure
   
   
6. Recreate the folder(s) you used in steps 1 and 2, making sure the path is the same. NOTE: If you were required to backup your Mail and WAB files to other media, you can restore them now.
   
   
7. Open Regedit and delete the HKEY_CURRENT_USER\Identities key.
   
   
8. Locate the 4 REG files you exported in Step 3 and import them into the Registry.
   
   
9. Open OE and enjoy.

Note: Your passwords for mail and news accounts will have to be reentered. These are not saved in the Registry.