Vista and Win 7 came years after PageMaker had been discontinued, so you cannot expect PM to be compatible with them. There have been reports of people who have managed to install PM under those OSs, with varying degrees of success. But I wouldn't risk developing or working in any important project in PM running in anything newer that XP. I would risk it if it was a matter of a few changes in a few files, knowing beforehand that it is very likely I wouldn't even get as far as installing PM. However, even for that I would fell much more comfortable using the free trial of InDesign.
So the answer to your question is really "it depends". It depends on what you want to do with PM, and how much you are willing to risk. In the long run, Bob's advise is the best.
Will Pagemaker 6.5
for Windows run on Win 7?
In an unstable way, if it will install in the first place.
Use Win2K for PM6.5, which must be getting on for 15 years old now.