When I first began working with Microsoft Search Server 2008 during the beta, I immediately missed the ability to create and manage global scopes at the SSP level. Exploring the various interfaces, it seemed that the default, All Sites, was the only one available and there was no link in the Search Administration page to create and manage other scopes that would be global across the SSP.
Digging around in the 12 hive layout files, I found the page that Microsoft Office SharePoint Server 2007 uses to manage SSP level scopes. By manually typing the URL, I discovered that MSS does indeed support global scopes. Someone simply forgot to add the link in the Search Administration page.
So, if you need additional global scopes, the URL is
<server>/SSP/Admin/_layouts/viewscopesssp.aspx?mode=ssp
or
<server>/SSP/Admin/_layouts/viewscopes.aspx?mode=ssp
Either one will open the management page for SSP-level (Global) scopes.
Have fun!