After doing a windows install on existing OS, windows xp is not very good in using existing User Profiles.This also happens when joing a new Domain.
To recover the old profile so you can get Outlook data and other Application settings, open the Registry Editor
Run > regedit
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProfileList
You will get something like S-x-x-xx-xxxxx…
Change the ProfileImagePath to the directory of your old profile : ie %SystemDrive%\Documents and Settings\your_username