Well I'm making progress, but there's still something missing.
Here's what I've done so far:
First, put the camera on code C5.
Delete all the ActiveHome software. Uninstall didn't work, so I just deleted it all. First it wouldn't let me because it was in use. I checked and the only thing I could see running was X10 net service. I stopped it, then I was able to delete everything in C:\Program Files(x86)\Common Files\X10 and C:\Program Files(x86)\ActiveHome Pro.
I rebooted.
I plugged in the VA12A and let Windows install the drivers automatically via Windows update. It seemed to work, but the camera still didn't work. SimpleVideo still just showed a black screen. So I went to Device Manager and told it to uninstall the driver and delete all driver files. Then I unplugged the VA12A and rebooted again.
I downloaded the latest ActiveHome Pro modules again, just to be sure, and ran the installs. When I installed iWatchOut, it asked me to plug in the VA12A. I plugged it in, and heard the sound of Windows installing a device. I looked on my taskbar and saw an icon for drivers installing, and popped it up. It said it was looking for a driver on Windows update -- I told it to skip that. The driver install then failed. Then I went back to Device Manager and saw "Unknown Device" with the yellow exclamation point. I opened properties on that, told it to update the driver, then told it to browse the folder C:\Program Files(x86)\Common Files\X10\DriverInstall\VA12A Video Capture\Vista64. It said it was installing drivers for a long time, long enough that I finally got tired of waiting and unplugged the VA12A, which made it fail. So I did it again. This time it succeeded. Then I opened SimpleVideo -- and to my great astonishment, I had video!
Then I went back to ActiveHome, and added a camera. Like I said, my camera is an XX30A, which is NOT in the list of available cameras. So I tried some of the others, finally settling on an XX17A. I had some trouble with it "flashing" at first, but restarting ActiveHome seems to have fixed that (or maybe it was power-cycling the camera, which I did).
So I added a second camera, this time a black and white XX32A, though I had to choose XX20A from the list. That also seems to work.
So I think it may actually be working now. I still have two more cameras to add, and of course I need to put them a lot further away than where they are now. But I think the hardware is working now.
Thanks for the tips! I'll post back when I get all four actually mounted and let you know how it went.
(And by the way, FWIW, there is no channel switch on these cameras. They do have the small rubber plug on them, but there isn't anything under it -- just the circuit board.)