It would be helpful if the Author added comments to the article and code, including what version he/she created this on and on what versions it is known to work. In this case its a pretty simple script, yet what sp_change_users_login does and how it works is still kind of vague. Of course I can google it, but it would be good if the Author addressed that, since its the backbone of the script.
BTW... msdn states that sp_change_users_login will not be used in future releases and advises not to include in new dev work
sp_change_users_login isn't something that you would include in your work, it is something you would use to DO your work.
That said, if you're running 2005 SP2 or latter, you might want to use ALTER USER [user] WITH LOGIN = [user].