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SP2 firewall by default does not allow icmp request. So either disable xp's firewall or go into the advanced tab in windows firewall, click on the settings tab in the icmp box and allow incoming echo...

I would start here:

http://www.cisco.com/en/US/tech/tk543/tech_topology_and_network_serv_and_protocol_suite_home.html

1)Is your wireless router pulling an ip from the cablemodem/ISP? If so-

2)Did you do all your Windows-updates when you were connected by wire to the cablemodem? If so-

3)Start uninstalling...