Most of you all would probably be knowing this, but for the newbie out there who is just getting into MOSS's Enterprise Search features this would probably prove useful...
Lets say that through the SSP Search Configurations page you've gone and created a couple of Scopes. But when you get back to your site collection you notice that none of the scopes appear in the search scope dropdown (normally located on the top right hand corner of the page), you only see the default scopes.
What you need to do is navigate to Site Settings page (_layouts/settings.aspx) of the top most level site and once there click on the ‘Search keywords’ link under the ‘Site Collection Administration’ section.
In the Scopes page you will notice that all the custom scopes created are contained in the ‘Unused Scopes’ section while the ‘Display Group: Search Dropdown’ contains ‘All Sites’ and ‘People’ while the ‘Display Group: Advanced Search’ contains only ‘All Sites’.
Click the ‘Search Dropdown’ link and add the Scopes by checking the appropriate ones. Do the same for the ‘Advanced Search’ link.
Once done, the custom scopes will appear on all search dropdowns in the site, however they will not appear on the default Advance Search page.
To get the scopes to appear on the Advanced Search page, navigate to that page (SearchCenter/Pages/advanced.aspx) and from the 'Site Actions' menu select 'Edit Page'. The page will now be checked out to you and be in the edit mode.
In the 'Advanced Search Box' web part click the 'edit' menu and then select 'Modify Shared Web Part'. The properties box for the web part appears. Expand the 'Scopes' section and check the 'Show the scope picker' option. Hit OK and the web part should update showing the scopes.
Remember to check in and publish the page so your changes will be seen by everyone who access the page.