I don't have multiple user accounts but I've tried both these techniques in other situations. They should work.
If it's just one or two, save them (File/Save as)
somewhere both users have access to. Logon as the alternate user. Double click to open the saved email (eg from explorer not O/E) then File/Move to folder.
If it's all messages then use File/Export from the old user and File/Import to the new user.
You may have to navigate to your message store. On mine it's
Documents and Settings/User name/Local Settings/
The gobbledeygook is a bizarre name like