Originally Posted by i2D__
You said all your other devices are fine, so I would rule out ISP as it would affect your whole house.. did you read my post above?
It's more likely that there's an incompatibility between his laptop and the Comcast gateway. I've run into that exact issue several times with the Comcast gateways over the past year or so. I've not seen the issue with the Technicolor gateways that they use, though, so you may want to ask Comcast for one of those if they have them available in your area.
Also, you need to check what type of encryption is being used on the Comcast gateway. If it's using, for instance, WPA/WPA2 mixed, then change it to WPA2 only. Let us know what you turn up.