Sudden Lag on Counter Strike: Source

Excuse me if this in the wrong forum, this problem is probably both software and hardware.
I play CSS a lot, and I'm in a clan. One of my clan members who usually had decent ping has suddenly had his ping go so high he can no longer play (it is now usually in the 300-500 range ). He sent out a post to the clan for a little help, and I answered with some generic stuff. I won't tell you what I've told him so I can get as many different responses as possible . All he's told me so far is that he runs on a wireless network. I personally use a D-Link AirPlus series Wireless router and DWL-G510 compatible NICs. Can anyone tell me any way to reduce his ping (I will say that I've already told him stuff like network traffic is bad, call the ISP.......but if you want to, repeat it for others with this problem).

 

thanks for the assist