The way having your info in a database would make writing a search engine easy, is that you can simply write sql queries to match keywords against certain table fields.
If your pages are static however, then you need other methods to read the contents of the rendered html pages, then match your search keywords against such contents using regex. That is not a trivial task.
One way you could save yourself a lot of agony is to let google search your site for you.
keywords site:www.yourSite.com
To implement this on your site:
Create a form with a GET method, and make the action:
http://www.google.com/search
For more details, go to php.net. Their form allows you to search via google.