C:\Documents and Settings\Admin\Local Settings\Application Data\Identities\{C4A1069D-4BFD-4C1C-BE88-717AC9CF8B9D}\Microsoft\Outlook Express is the 'normal' place for outlook express to hold your various outlook express 'folders'. I assume you DO mean outlook express, not the professional XP outlook package?
In that location (which you may need to go into folder properties and make 'system files' visible to see at all), are a number of files with a .dbx file type. These correspond to the 'folders' you see in outlook express itself.
Basically, all you need to do is make sure that in your 'new' copy of outlook that you first create a 'folder' to match each of the names you find in the original set of names. Then just copy the old files on top of the same names in your new location.
If you miss one, although the file - lets say - aunties.dbx exists, you will not see a 'folder' aunties in your new outlook express, and if you then try to create it, you will just create an aunties[2].dbx and so on. Silly, but then so is outlook express.