Michelle,
My advice is to avoid such a project. Search engine in php is not such a good idea, unless you want to do it for educational purposes.
I would suggest that you get mnogosearch or htdig and let these index and search your site. Both are written in C (I think), so they'll beat PHP in speed and power.
If you still want something that is "homebrewed", than look at mysql manual and read about full-text search option of mysql.
Di
