In SharePoint 2007 there is a search scope dropdown:
This is missing in a default setup of SharePoint 2010:
It’s still available, you just have to turn it on. Just go to Site Actions, Site Settings, Site Collection Administration, Search Settings:
Note that this is a site collection setting, not per sub site.
Select “Show scopes dropdown and it’s back!
This was an option only in MOSS 2007. WSS 2007 always had the scope dropdown. I have not checked SharePoint 2010 Framework yet to see if is an option there…