Internal Website search facility

Hi all, I hope someone can help!!!

I know this is the wrong place to ask this question but I can't seem to get a straight answer anywhere else.

What I am trying to find out is whether there is a way of adding a search facility that is restricted to a particular website's content without having to put all the content onto database format.

I.E: you have your normal menu system but you can also search by a particular subject or keyword.

If there is, is there any open source software or code that can be inserted into your website to achieve this. Or where would be the best place to ask such a question.

Heres hoping. Many thanks

Richie