If you are asking whether it is legal to run a 32 and 64 bit versions of Win 7 using the same key, I have seen opinions on both sides. Therefore, no definitive answer from where I stand and there probably won't be until someone goes to court. I wish Microsoft would have listed some of the standard no-nos, but they have not.
If you feel it is legal, it has been suggested that you might wait 30 days after activating the first install before you activate the second. Will it even work then--I have no idea.