But rightly or wrongly I run full NAV and Internet Security which do slow down the start up process. Can I run programmes such as Spyware Terminator and others in parallel with NAV+IS without either rotting up NAV or NAV interfering with them?
Possibly. I've read of a user with SpywareTerminator and NIS 2007 that was then unable to connect to a certain site, troubleshoot still ongoing.
Norton is more likely than a lot of the other security programs to not play well with others.
If you try another resident program, like ST, make a restore point first, just in case.