CS5.5 and CS6, please (which are InDesign 7.5 and 8.0, respectively).
Yes. No problem at all.
Many people consider it fairly important to do this, because of the lack of perfect backwards compatibility.
Some will advise that it's important to install them in order CS5.5 before CS6.
My experience is that has not been necessary since CS3, but it's hardf to give guarantees.
Europe, Middle East and Africa