I figured out how to stop the darned reinstaller when you try removing CAV.... try the steps below:
When registration of the engine is corrupted, all attempts to run .msi packages fail.
To correct the registration of the Windows Installer, unregister and then register the Installer service using the command line switches shown below. This shuts down and reregisters the service, which assures that the Windows Installer engine should function properly. Enter the following commands from a command prompt:
msiexec /unregister
msiexec /regserver
I had tried getting rid of cavemsrv.exe as well and got the same problem with it trying to reinstall. I just clicked cancel until the system came up and went to ADD/Remove and uninstalled CAV and reinstalled it after.
BTW, I had bought a copy of NAV 2006 and when I had wanted to try another firewall it wouldn't let me uninstall the old one, even AFTER I had uninstalled NAV 2k6. I eventually had to reinstall Windows to get rid of NAV 2k6 alltogether. I brought it back for a refund. NAV is bloatware and crap.