What sort of search are you intending here? Google has a program for what they call Personal Web Search or something like that. You need a developer key, which is free, but which is bound to a single domain name (per key). And then you need a lump of JavaScript that will interact with their server and do clever things like only search a single site. We used it on this (FreewayTalk) site for a few weeks while Sphinx was being configured. It works pretty well, although you rely on Google to make regular re-indexes of your site, and that’s not always an immediate thing.
If you just want to add a Google search box to your site, essentially duplicating what you would see on the home page of the Google, then the code is pretty simple:
Paste all that in a Markup Item drawn on the page and you should see a Google Search when you preview or view the site in a browser. Make sure there are no other forms on the same page, or you page will be invalid (can’t have a form inside a form).