funny thing. i can reproduce it now. i’m using the exact same disc image and avast installer file as before, in VPC2k4, you can run a VPC without ever commiting any changes so each time you do a cold boot of the VPC, its reverted back to the original hard disk image. So, I can say nothings changed for sure. Anyway, I ran about 10 times, reverted each time, and its reporducable every time. The installer does not write to the VDD key. Here is all regmon picks up during the install, right near the end:

5674 79.67422089 avast.setup:452 OpenKey HKLM\SYSTEM\CurrentControlSet\Control\VirtualDeviceDrivers SUCCESS Access: 0xF003F
5675 79.67447790 avast.setup:452 QueryValue HKLM\SYSTEM\CurrentControlSet\Control\VirtualDeviceDrivers\VDD SUCCESS “”
5676 79.67462904 avast.setup:452 QueryValue HKLM\SYSTEM\CurrentControlSet\Control\VirtualDeviceDrivers\VDD SUCCESS “”
5677 79.67476984 avast.setup:452 QueryValue HKLM\SYSTEM\CurrentControlSet\Control\VirtualDeviceDrivers\VDD SUCCESS “”
5678 79.67489332 avast.setup:452 QueryValue HKLM\SYSTEM\CurrentControlSet\Control\VirtualDeviceDrivers\VDD SUCCESS “”
5679 79.67513944 avast.setup:452 CloseKey HKLM\SYSTEM\CurrentControlSet\Control\VirtualDeviceDrivers SUCCESS

Not WRITEs. I tried running it with and without the preexisting 2 null bytes,