You need to add that user's network logon ID to a group that has the proper authority to install software.
Logon to his PC as admin, right-click 'My Computer' and click on "Manage."
When Computer Manager comes up, click on 'Local Users and Groups.'
In the right pane, double-click on 'Groups.' You will get a listing of user groups that are contained on that PC.
If you don't want him to have full admin capabilities on the PC, double-click the 'Power Users' group, and click 'Add...'
In the 'Select Users or Groups,' make sure that your domain is selected in the field labeled 'Look in.'
The users from that domain should appear in the listing below.
Select that user's logon name from the listing and click 'Add.'
You should be returned to the Computer Manager screen. Close out of everything, log off, and have the user log in. He should have install capabilities now.
Note: You can perform these steps from your server or your workstation (NT or 2000), but you must be logged on with the credentials that has admin rights for the PC that you are connecting to in order for it to work. You would just need to connect to the PC through the mmc on 2k or use the User Manager for Domains and "connect to domain" - (domain being the computer name of the workstation you are trying to administer).