The Keyspan USA-19HS USB/Serial adapter appears to work fine when used with Windows XP, on Bootcamp, on a Macbook.
The driver that came with it is 3.4. The latest driver on the web site is 3.7s. I initially loaded 3.4 and then updated that to 3.7s which worked without issues in the Bootcamp environment, but produced some unexplained complaint in the Parallels environment.
With the 3.7s driver, Live Video Settings Editor works without a hitch to Get and Load the Video Source Adjust menu settings.
So I did a Load Saved User Settings (to get the Video Source Adjust stuff back), used Live Editor to save that to the Mac, and then re-did the firmware install. It too completed without complaint. Then the 30 second power cycle, reload factory defaults, reload saved user settings, and Open and Load the saved Video Source Adjust settings from the Mac. Again, no complaints. For good measure, I did another 30 second power cycle.
Unfortunately, the Video Source Adjust menu settings still revert to defaults when you power cycle.
I'll just have to try to work this with Anthem in the morning.
But for folks planning on using an Intel-based Mac, my advice now would be to use Windows XP on Bootcamp with the Keyspan USA-19HS adapter.
ETA: This Mac itself is running Leopard 10.5.2, fully updated, but I doubt the Bootcamp environment depends on any of that.