Adding Boolean AND & OR to a PHP/MySQL search page

I have a PHP page that searches a MySQL database for three drop-down boxes and a keyword field (i.e., users can pull down region, theme, and scale, and enter words into a textbox before hitting submit).

Everything works nicely, but it defaults to a Boolean AND when entering multiple keywords. I’d like to add basic OR functionality, and if possible, the ability to accept quote marks and wildcards.

Is this a relatively straightforward change or something I’d be well enough leaving alone? I’m a hack, a build-it-as-I-need-it cobbler, so I have a mixed set of skills which is somewhat bothersome because it’s hard to tell when I’m getting in over my head.

Thanks!

Rhythm