You can set up a domain user in Plesk 5.x (MDH and Upipe hosting accounts):

1. Click on the domain name for which you wish to set up a domain user.
2. Click on the Domain User button.
3. Check the box next to "Allow Domain User Access".
4. Enter a password in both password fields for the domain user.
5. Click on the Update button.

To set up a domain user in Plesk 7.x (OHP and WebPro):

1. If the account is a WebPro hosting account, click on the System tab. For the OHP hosting account go to step 2.
2. Click on the domain name for which you wish to set up a domain user.
3. Click on Domain User Administrator.
4. Check the box next to "Allow Domain Administrator's Access".
5. Enter a password in both password fields for the domain user.
6. Set the Preferences and Permissions you wish this user to use.
7. Click on the OK button to save these changes.

The domain user now can log into the Plesk Administration control panel using the name of the domain as their user name, and the password you supplied. The login URL will be:

http://domainname.com:8443/

Where you replace "domainname.com" with the actual domain on which you have configured domain administrator access.