Federated search  becomes available when you get to MOSS 2007 SP2 or later.
But are you sure you need federated  search? Federated search is used to
provide search results form other search engines in a web part next to the
SharePoint search results. MOSS 2007 can crawl and index external  websites
just like it crawls SharePoint content if you create another content type.
In that case the results are included in the SharePoint results set.