Booleans can be a right royal pain...but they do have uses and you do need to plan ahead. Sometimes its just as easy to split poly what you want, delete face etc etc. Tweety is right though...delete history before you try it..or as he said extract the face you want to boolean then sew it back up. I have also found that boolean over an edge through the middle...if you dont you wont be able to split poly to clean it up...it wont start an edge on a hole...but if you have one there first it will...go figure.

cheers bullet