“Custom Site Definition” is a free download at mindsharp.com in the premium content section.

I need to search documents in a document library. The
search needs to be done on metadata(stored as column
in doc library).

How can i achieve this.
any help  is appreciated

I sent them to Advisor when I wrote the article  and have told them twice
that the links are broken but for some reason their Web site  links
continue to fail. You can download the files  from the Premium Content
area of the http://Mindsharp.com site.

I can't give the exact link as I'm offline right now. Let me know if
that doesn't get you the files that you need and I'll give more granular
step-by-step instructions.

in my downloadable  example I include all the modified pages that
optionally handle an alternate header. This required an edit to every
direct-mode page in the custom site  definition (which is why I include
it in the downloadable version - to save you the time). So, every page
includes server-side script to accommodate an alternate header. This is
not a problem in my ghosted-only pages shop. But, if any page in these
custom site definitions were to become unghosted, the entire page would
fail.

In the article  I explain (although perhaps without enough vigor) that I
do not like the alternate header. This is one of the reasons why. There
are step by step instructions in the article that walk you thru how to
create your own custom site definition  sans the alternate header.