The Vatican has specifically issued several warnings against freemasonry. The older freemason organizations (mainly in Europe) are specifically and explicitly anti-Catholic. Most masonic lodges claim they have no specific religion, but in so doing they also disavow Christianity. And freemasonry actually seems to espouse some kind of "naturalism" which denies the divinity of Christ and is thus also opposed to Christianity.
I think Dacs posted some Catholic Church documents about freemasonry already. The bottom line is that you cannot be a freemason and a faithful Catholic at the same time. Correct me if I'm wrong, Dacs, but I think to become a freemason is to incur excommunication.
God bless!