I have a D-Link modem and I tend to have lagging problems aswell. I have AT&T high speed internet, which I would like to recommend
I found that moving my PS3 closer to my modem gives me really good speed, even if other people in the house are using the internet.
As for your computer problem, I use this wireless adapter that helps me pick up internet connection from my brother's room since our modem is really weak. I was thinking of getting a better modem so that my wireless connection won't be so weak.