I've had ZoneAlarm and Norton Anti-Virus running side-by-side without any troubles at all. The only place they may conflict is when checking emails for malicious attachments, but all you have to do is turn one of them off (I turned off ZoneAlarm's email checking).
Unless you get a hardware router that checks both inbound and outbound connections, you will still need a software firewall on every computer. Most consumer hardware routers/firewalls only protect you from people on the net trying to get into your computer but will not stop a Trojan running on your computer from getting out. These routers are designed with the assumption that anything coming from your network side to the internet is legitimate and safe, which unfortunately, is not always true.
goates