Search engine : build a new one or use an alreadry existing one ?

Hi, I need to improve my current "search mecanism" but got stuck in a dilema : build one or use an existing engine? My site, that uses php/smarty allows my users to browse products in a category listing or search. Currently my search only performs a 'select xxx from where field like ' and show the results. Even tough it works I'd like to improve it, showing the results by relevance, proper hadling mispelled words, performing the serach not only in the product's name etc. I've tried mnogosearch but I am not sure that I'll be able to manipulate the query results in order to show only results in the product section (not the entire site). Regards, rt