This is simple if you are using Outlook Express for both accounts.
All messages (inbox, deleted items, sent items) are stored in a folder under each user account.
1. Log on to the new user account and open outlook express.
2. Go to File>Import>Messages. Choose Microsoft Outlook Express from the list, click next.
3. Choose "Import mail from an OE6 store directory, click next.
4. Click on the browse button.
5. Now you have to find the store directory. First make sure you have your hidden files visible. Then find C: Drive>Documents and Settings>Administrator>Local Settings>Application Data>Identities>Some long gibberish file name>Microsoft>Outlook Express.
6. Once that Outlook Express file is highlighted, click next and it should start importing your messages.
Let me know if this doesn't work. I have done this many times and sometimes the folder setup is a little different.