I'm not an expert so bare with me.
The bare bones of logging in: there is a form with a username and password field you fill in and a submit button.
The info you submit is sent to a script which find the username in the DB and compares the MD5 of the password submitted to the MD5 of the one in the userdatabase.
The names of the values of the fields change from program to program but the general jist of it works.
So why not call the username field 'apple' and the password one 'orange' and write a small, tiny winy script that includes the login script for wordpress and whatever other program you want ( my intention is phpBB ).
The 'apple' value is then stored as 2 identical varibles with different names, the one the WP login script uses and the one the phpBB uses.
Since the scripts has the values as varible names they originally wanted why can't both individual login script be used in this same program one after the other since they are both getting the info they wanted?