Have you read through the content at
technet.microsoft.com/en-us/library/cc303314(TechNet.10).aspx ?
WSS is different in that there are no SSPs and that typically means no
"Application Server", just WFE(s) and database(s). There are also a lot
fewer services  - basically only the core product and WSS Search both of
which are typically run  on all WFEs.

This means we cannot have a separate application server  for running
the Query or index services  as we do in moss  environment?

Those are not separate roles in WSS - there is just a single "search"
service. Since WSS search only indexes WSS content on the local farm,
the need to separate the roles out isn't really there.

You can have a search server  that is not your Web server, but it must host the
IndexQuery role as those cannot be seperated, as Brian said. that's about the
extent of farm  scaling with WSS. You probably don't need multiple WSS search
servers as it uses the change log for incremental indexing and is *usually* very
efficient. Also beware that content databases are associated with WSS search,
whereas MOSS search associates URLs. These are detailed in the ms press
sharepoint pocket consultant.