What I'm saying is that if the keylogger is only on the host PC, the logger has no info about the guest system, and unless it's doing the screen shot stuff, how will it know you were entering a password. This is provided you design the Virtual PC to not use network connections, or can only talk with the Host OS and nothing else (with the two OSes being different, like Linux and Windows).
Let's drop this though for now, too much work is needed for too little gain in the long run.