Hi,
I have a 4 port router to share my ADSL connection which claims to have a built in firewall. My friends advise me that I should be running a firewall to monitor inbound and outbound network traffic and so I have installed the free version of Zone Alarm. This warns me when any software tries to access the internet so that I can choose to allow this or not. However do I really need a software firewall, should I be able to configure my router to do this for me? Is it that one needs both hardware & software firewalls? Maybe I don't really understand what it is I really need, any help would be very welcome.

The more protection the better, in my opinon, especially if you're using an "always on" broadband connection, and even more so if you have a static IP. You can set up your router's firewall through the browser interface, usually by opening your web browser and punching in the address of your router (192.168.1.1 is a common router address for subnets).

>>Is it that one needs both hardware & software firewalls?
All you need is a hardware firewall if it's an actual hardware firewall and not a router with firewall support. If you don't have a "real" hardware firewall then a good software firewall to supplement the router firewall is a good idea.