If you are upgrading (ie. installing XP over 98SE without reformatting first), then all your folders, the address book, e-mail accounts, etc, will be automatically saved and moved/imported accordingly.
If you are doing a fresh installation of XP (which is always the professionally recommended method), then you'll need to do the following backup procedures first:
Outlook Express -> Tools -> Accounts -> Mail
hi-lite each account in turn, click "Export"
This will save each account to an .iaf file (Internet Account File)
Save these .iaf files later to a backup floppy or cd-r (or into a backup folder on a different hard drive, if you have more than one)
Save the .wab file and your .dbx folders to the same backup location.
Just to confirm:
The OE Folders in Win98 are stored wherever it says when you right click the folder in OE and select "properties".
This is usually in a subfolder in:
C:\Windows\Application Data\Identities\.....
The Address Book .wab file is usually in:
C:\Windows\Application Data\Microsoft\Outlook Express\..... or
C:\Windows\Application Data\Microsoft\Address Book\
Finally, if you've created any extra folders/subfolders in OE other than the default ones (Inbox, Outbox, Sent Items, Drafts, Deleted Items), then take down a note of your folder tree. This will become more evident later.
Now that you have everything backed up, after you've installed XP, open up OE
Assuming the Folder List is viewable in the left pane (if it isn't, go to: View -> Layout, and checkmark "Folder List") . . . if you did previously have any extra folders, recreate your original tree now (right click on "Local Folders" -> new folder, or rt click relevant subfolder -> new folder).
Now go to:
Tools -> Accounts -> Mail -> Import
Browse to your backed up .iaf files and import your accounts.
To import the address book, go to:
File menu -> Import -> Address Book
Browse to your backed up .wab file
Now, all that remains is to import all your folders and saved e-mails.
Completely close Outlook Express.
Open the folder where your backed up .dbx files are
Now open another Explorer window and go to:
C:\Documents and Settings\(your user name)\Application Data\Identities\{some-big-hex-number-here}\Microsoft\Outlook Express
Copy & Paste all your .dbx files into this folder, thus overwriting the existing ones.
Reopen Outlook Express, and voila!
Hope this helps
btw, Microsoft's instructions are here
http://support.microsoft.com/default.aspx?scid=kb;EN-US;270670
But my method is much better, heyhey
I strongly advise that you make two backups of everything, just incase something like
this happens.