Worth Installing a firewall?

[Jimbo]

I have a Netgear DG834G router and I belive this has a built in firewall. So I dont use one apart from this, is it worth using something like Kaspersky internet security?

 

[Jimbo]

Thanks for the help. I have Kaspersky anti virus 6 installed and it does a great job in virus stakes. I allways turn off windows xp firewall as it is carp, I think I'll prolly leave it at that, seems to work ok.