Ok, to log into his account, you need to re-set his password.
To do this, go the, "Find/Edit/Suspend User" Type his name, and then click on edit details. There is a box to enter a new password for that account. Rnter anything you know or can remember and then submit your changes. Then, only you, and not that member have the password for that account. That allows you to take control over the account until you tell him what the password is.
Majicman
