1) First to make WSS Search crawl forms based authenticated sites by taking following steps:
1.1. Extend the form-authentication web application to a zone with windows-integrated authentication (NTLM) enabled.
1.2. Make sure if the search crawl account has access to the new web application, else Grant Permission.
NOTE: The crawler will access to the site content through this “secret” NTLM web application. It will be able to get the form authentication descriptor of the content. After the crawl’s completed, you will see search results in your form-authentication site. It’s important to know that the URL of search hit will be based on your form-authentication site, because it’s depending on where you are searching from.
2) Using Central Admin configure the Search Server .
3) Attach the Search server to the Web App.
4) Finally configure scopes and permission level search at site level.
5) stsadm.exe -o spsearch -farmserviceaccount domain\admin -farmservicepassword password
stsadm.exe -o spsearch -farmcontentaccessaccount domain\admin -farmcontentaccesspassword password
6) Updated the zone to default for the extended web application.
Refn: http://gj80blogtech.blogspot.com/2009/08/wss-search-configuration-administration.html
