I've seen these two resources:
But it looks like #1 is out of date, and #2 has too many constraints (maximum resolution, limited size of desktop).
I was using NoMachine client/server for this purpose, but new versions of NoMachine's software don't permit this with their free versions. (Maybe it's time to request a license?) Also, our new officially sanctioned Windows boxes (the client) are locked down even more, so the client must be a portable app, i.e., doesn't require administrator privileges in order to be installed or to run.
Also, I did get the free portable version of NoMachine's NX client to connect to FreeNX on Linux, however resuming sessions didn't work, which might be a deal-breaker.
Any other ideas for getting multiple displays to work between a Windows client and a Linux server?