I'll have to check my (Vista) IP when it happens. Though when everything is up and running if I log my mobile off then on (to my secure router), I don't get the IP address in the range I've specified in the router i.e. I should get a 2.101 through 2.105 but I get something completely different 184.108.40.206, so I'm thinking that his computer is assigning the IP's through his DHCP?
If I can pry him off Second Life for more than 2 min I can check what IP he has when his computer is the first on the router and mine after I log on. This would be proof enough that it has something to do with his computer if the IP range is the same as his I'm thinking.