Are u using MOSS or WSS

If MOSS then out of box it comes
with such a configuration

I am using Moss.......................

http://www.apps4rent.com/sharepoint.html

Implementing search  is very easy.By default MOSS indexes word  documents. If
you want to search through PDF documents install either adobe pdf filter or
FOXIT filter and index the documents.After you crawled, the documents will be
listed in the overall keyword site search.
Implementing Custom site search:
Create scope.Write a custom search query and return the values using the
webpart.
This is all w.r.t to MOSS 2007.All these settings has to ne done SSP of that
site.

FOR WSS 3.0:
There is no scope of SSP.
1. You can still implement  using custom code using search query.
2. Install Microsoft search server express 2008 and implement search as MOSS
2007.