Edit the properties of the users you wish to now show up in the GAL. On the General tab click on the “Hide from Exchange address lists” check box and click OK.
You do not say what version of Exchange. For Exchange 2003 you will do this through ADUC, for Exchange 2007 you do this through the Exchange Management Console.
The tabs in AD are indeed no longer available with exchange 2007; thus, there is a product that allows using the tabs again – exchange tasks 2007 @ http://www.u-btech.com/products/exchange-tasks-2007.html
If you have users appearing in the Global Address List and they are not Mail Enabled (Exchange 2007) then chances are you probably created a user in Active Directory which was mail enabled and then copied it to create a user that you don’t want to be mail enabled.
If you have a user in the Active Directory and when going into Exchange Management Console they do not appear anywhere but they are in the Global Address List all you need to do is amend the attribute ShowInAddressBook under the user in Active Directory.
You will need to ensure View Advanced Features is ticked on in Active Directory Users and Computers and then double click on the user to display the properties. Click on the Attributes tab and then scroll through the list and look for ShowInAddressBook and click on Edit and remove anything that is in there. Click apply to the changes and bingo they have gone.
Hope this helps