We check if the versions aren't compatible if you use the installation CD, but in this case Ernie sent you a ZIP file via e-mail of only the EXE program and Version.ID which counts on you already having the latest Galil Version 7 drivers installed, plus the WSDK was installed afterwards and they don't check. They just re-register the card by pointing to them. Hence your problem.
Use regclean.exe to clean the registry and follow Al's post just to be sure and install the WSDK first then contact us directly to get an installation CD for V15.9 sent to you. Our installation CD will sense the WSDK installation and allow the drivers to be shared, plus it won't re-register the card if it see's the WSDK.
Unless they came out with something new very recently the two are compatible and is what you should be using.
You should not setup 2 XP copies on the same PC.