Setup found another antivirus on your system

Just downloaded and trying to install the Home version. I get a message box with these contents.
Setup found another antivirus on your system.
If you decide to install this program it may conflict with tfollowing programs: Norton Antivirus / Internet Security
Continue?

I´m used a system just with AVG 6.0 and the rest of the NSW 2003 suite (NOT NAV).
I have used a lot the jv16PowerTools (it´s a great application) but nobody can be free of NAV and Symantec keys. Symantec just corrupt your registry. Nobody could say nothing agains this! :o

Avast continue not working well in my system. It blocks the DOS programs under XP.