IP Routing question w/ winxp

I am using a wireless cable mdm with built in router/nat which auto assigns ips 192.168.. to my computers. I used whatismyip.com to get the real ip, let’s call it “a”. my computer ip is “b”. Since there is no way to access the modem like a regular router to configure ip forwarding, can I use the winxp route command to route “a” to “b” so I can host internet games? Thz for any insights.