If you would like to be able to select which OU to import from in your Active Directory then select Custom Source in “Configure Profile Import” in the SSP settings. That will let you write your own custom source like the following example:
The default setting is DC=yourdomain, DC=se so what you will do is to put the OU in front of the DC since it must be in a hierarchy.
Cool! So instead of importing 400 accounts from your AD you get the accounts that are relative to your site!