How to default to VM#1 or VM#2

I have 32bit Win7 in one VM under Parallels 7, and
I have 64bit Win7 in a second VM under parallels 7.

When I launch Parallels I am not given a choice about which VM to open. Usually both VM's open.

I am sure there must be a way to have Parallels default to one or the other of these VM's, but I have not found anything in Preferences.

Can someone help ?

By the way, I installed both versions of Win 7 in order to determine which works better under Parallels 7. So far, I can't see any difference. Am I missing something ?