Linux user talking here
On the hardware side, maybe your buddy should check for the latest GPU and network chip driver. It's also never too bad to have them up to date.
On the Internet side: be sure he doens't use the network for some other tasks (updates, downloads, ...). I've also heard about some recurrent issues with some Internet-cable users; it's often because another users is using all the bandwidth on the wire you share with him. Sadly, there are no other way than to change to a phone line connection which means a new ISP in most cases.
I also remember when my wifi had some perturbations with some other wireless system (cold war like). I had to change channel to get it right. But it was with all kind of communication (ICMP, HTTP, etc.). It was fun to see all those packet drops and retransmissions
Lastly, check if he has this problem only with SG or any other network game (which then uses UDP). If the problem is there, check the option of your modem or router to be more friendly with UDP traffic. If nothing works (and you're sure it's network related) maybe getting a phone call with your ISP might solve the issue.
"Chuck Norris had to shorten his beard in the presence of Richard Stallman because two beards that awesome, so close would segfault the universe (again)."