Anti Virus Protection

[Tartan Giant]

Hello guys,
I am presently running TWO anti-virus programmes on my pc thinking of the "belt and braces" principle
1) Norton AntiVirus 2000
2) Trend PC-cillin 98

Is this a daft thing to do, in that they may interfere with each other, and are doing the same job anyway ?

They are both set to scan on start-up and they appear to co-exist.

Thanks guys.