Using the Google Search Utility on your site

The Google Search is a good site search tool. If your worried about people using it to search the web and leave your site you can install your own site search script.

There are and will me tons more but if your own search does not turn up anything that interests you try  Fluid Dynamics Search Engine it has a freeware usage and you can purchase it for $40 if you like it why not buy it.

For medium sites up to around 500 pages this will do the trick.