"I am running vs. 10 on Windows 7 with 64B processor. Also, Windows 7 reports incompatibility with PGP."
I did have a customer report this same behavior. However, I have been running natively on Win7 64 bit since early last year. We ended up determining that it only affected the machine he was using. (In other words the othe Win7 64 bit systems in his environment did not complain.)
PGP Desktop will not shred a shared drive across a network. This is a design decision.
If you have some sort of adapter cable (SATA or IDE to USB) or external enclosure, you could use that to attach one system's drive to the other. Since this would not be across the network and would not be the system drive, PGP Desktop should allow you to shred either the free space or the entire drive.