There will almost certainly be conflicts, NAV doesn't coexist well with other AVs. if you try to install avast on a system that has NAV on it already avast will most certainly detect it and disable some of its elements to avoid any conflict which might lock up your system.
Even after NAV is uninstalled it has been notorious for remnants left behind, which can cause issues.
A link worth looking at, which is a program removal tool that can remove the remnants of a number of different Norton Programs:
Removing your Norton program using SymNRTYou can also download
SymNRT, a Norton uninstall tool that uninstalls all Norton 2004/2005/2006 products.
This would ensure all of NAV was removed and avast could run without problem, the one thing you would most likely notice is things speed up as reported by many who have made the move to avast!
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