Hi Karen!
Not much of info in your Q. So the A may be usefull or
not...
If you mean the use of the Windows Update link in the
start menu, it always uses windowsupdate.microsoft.com.
SUS_SP1 can't (so far) be used manually.
You though can disable the use of the Windows Update link
using GPO.
If you mean the fully automated SUS & Client you must use
GPO (wuau.adm), or make registery entries to the client.
Also the SUS server must be configured to store the
patches and to function as the update server. RTFM
There is a newsgroup for SUS:
microsoft.public.softwareupdatesvcs
Cheers & Peace
EBE