Firewall and Linksys 802.11 Wireless Password

Does enabling Windows XP or MacAfee Firewall cause a change to a Linksys Wireless Router setup? I changed my wife’s desktop computer setting — it’s the computer connected to the router — to enable the Firewall and later noticed that my laptop couldn’t get on the network via a 802.11 g connection — it was newly changed to “Security Enabled”. I changed firmware, went back to default settings and disabled the Firewall, but wonder if I can re-enable the firewall. And if I need to set up a password, where the heck do I create that?