try instlling the PM7 demo and convert them to the newer format.
I have Pagemaker files I open here all the time with indesign cs4 this is on a mac.
If you will try opening them here if you like. I can then save them as cs4 for you.
Just tried opening a pm6 file with indesign would not work
Renamed file from .pm6 to p65 and indesign would open it (yes i lied to the program)
Given the symptoms I'd say the files are toast.
Thanks for everyone's help. I took the disk home with me where I have CS5 and it opened them once I forced it. CS3 would start to open them then crash. So now I have to save down to CS3 in order to deal with them at work.