I'm not an expert on LIKE queries, but I would do this:
break the search string up into the different words (explode(' ', $searchstring) perhaps?).
loop through the array building the LIKE part of the query
add this to the main query
for instance, if someone searched for "hot fudge sundae", the LIKE string would be:
TITLE LIKE '%hot%' OR SUMMARY LIKE '%hot%' OR
TITLE LIKE '%fudge%' OR SUMMARY LIKE '%fudge%' OR
TITLE LIKE '%sundae%' OR SUMMARY LIKE '%sundae%'
may not be the best way, but it should get the job done.