The .pst file (or personal folders file) is used by Outlook to store essentially everything you see when Outlook is open (saved email, contacts, calendars, etc. The .pst file is primarily used in conjunction with Internet email, but can also be used in conjunction with Exchange.
The .pst file is normally found at C:\Documents and Settings\\Local Settings\Application Data\Microsoft\Outlook. By default the Local Settings folder is hidden because its contents are considered system files. You must change this setting in Folder Options (Windows Explorer Tools menu) in order to find the .pst file.
The .pst file is specific to the email profile for each user. When you created a new user account, even though it had the same user ID, as far as windows is concerned, this was a new user. Therefore a new user profile was created. A new email profile must be created for this new user profile. The user's email was not deleleted it still exists in the the old user profile.
You can fix this in one of two ways (this assumes you have already created a new email profile for this user:
1. Copy the .pst file from the old user profile to the same place in the new user profile. If the old .pst file has the same nameas the new .pst file, it will overwrite the new one (and delete any email saved in the new one) when copied.
2. In the new email profile, delete the current Personal Folders file, and reinstall, pointing to the location of the old .pst file.
Hope this helps.