Subtract is an option for nurbs booleans. I was assuming he wanted it to be in polygons, so I gave him Difference, which is the same as subtract - only it's for polygons.
And if you can't get it to work try doing one letter at a time. Maya will be stuburn with the boolean command from time to time, so it may take some tweaking. Try deleting your history after each boolean for instance.
Izzy - lol. Sorry, don't mean to scare ya' dude! Don't worry though. It's only a bunch of pixils aligned in such a fashion as to resemble my face with 50% of the colors being inverted. Think of it that way instead.