Routers almost always have built-in NAT support which acts like a firewall to block port access coming inward. I presume your router is set to UPnP so LW communicates with the router to open a listening port whilst LW is open. There is a chance the UPnP is not working properly with the laptop for some reason.

AFAIK I believe it is possible to port forward for the 2wire device just for the laptop, whilst the desktop can still use UPnP. That's guessing from port forward instructions I've seen for 2Wire. But we'd need to know your 2wire device model number.