There's two ways. In and Out. XP firewalls block incoming but not outgoing. BUT you only have to worry about blocking outgoing if you don't run a virus checker on email or don't run a pop-up blocker. If you don't let a trojan install or virus get you you're okay with XP's firewall. That grc guy goes waaaaaay overboard in scaring everybody. According to the rfc's your machines ports are supposed to respond to pings and not be in stealth mode. But XP's firewall will put you in stealth mode which is fine. I don't know what you're running. Just don't panic. Get a firewall. If you're on XP you have one already just enable it. Be a little careful with ZoneAlarm...it's great, but it hooks into everything. Run a virus checker on your mail. And to stop popups something as simple as Proxomitron (a proxy server) can do it for you with no muss. I'm sorry, no links. T-storms on the way so I'm outa here. But Google is your friend. I highly recommend Proxomitron. It's free and brilliant.