I uninstalled NAV 2004 using only Add/Remove and so far (touch wood) I have not had any problems with avast! I have eliminated all folders associated with NAV. But I have noticed there are still some entires in the register referencing Symantec.
I don't feel comfortable with the regedit and I didn't feel comfortable using the Symantec tool because one of the steps is to reload a MS file scripten.exe. Not sure what Symantec does that means this is necessary and not sure what happens to my system if I screw up.
I don't know too much about this integration between Symantec and Microsoft but they are joined in many fields...
Look at C:\Program files\Common files too (if you did not see yet).
This external control center is unknown to me but maybe I could safely use it to get rid of the registry entries???
Yes it will. RejZor uses other avast users information and his knowleadge to do that great piece of software. You can trust it.
Or maybe it's Ok to just leave them if they aren't causing me a problem with this great
product. Any info would be appreciated. 
It's wrong. Some Symantec keys will
in fact and for sure make harm to your system. You won't be protected with avast in all situations (for instance, using a cmd window, DOS, under XP). Can you
see the contents of this Registry keys and post them here?
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\VirtualDeviceDrivers
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Control\VirtualDeviceDrivers
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet003\Control\VirtualDeviceDrivers
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\VirtualDeviceDrivers