fulltext mysql search formatting and preg_replace question

hi there i am creating a fulltext mysql search engine, i am generating the sql query from form inputs , within a fulltext text field , i can input exact matches like so "something1 something2" "something3 something4" , although there is a problem with this , the server defaults space between words to OR , althought he user may require AND so the syntax is like "something1 something2"+"something3 something4" or even +"something1 something2" +"something3 something4" this isnt really user friendly , i was wondering what the best way to format this to a friendly search syntax , maybe like this "something1 something2" AND "something3 something4" or even "something1 something2" OR "something3 something4" and formats it like +"something1 something2" +"something3 something4" if there is an AND statement or "something1 something2" "something3 something4" if its OR where AND/OR are in a select menu , i'm trying to format all text with "something" around them using preg_replace so it should be +"something" any ideas ?