I am using Sharepoint Server 2007 for search  (not the full  version,
SharePoint Server 2007) so I hope this applies to your problem. Do you
have show scopes  dropdown enabled in the Search Box web part? If not,
do the following on the Search Enter page:
Site Actions --> Edit Page
On the Search Box web part, click Edit --> Modify Shared Web Part
On the resulting Search Box modification applet, expand Scopes Dropdown
section
Click in the dropdown  mode field and select "Show scopes dropdown"

Actually, I found and resolved the issue. The show
scopes dropdown  was enabled in the search  box web part. In the search
box web part properties, though, under Miscellaneous, the name of the
scope display  group the web part was looking for by default was 'Search
Dropdown'. Once I set my scope  display group  to match, it all worked.