Every time I connect (tether) my iPad to the PC, the PC loses it's WIFI connection to the router. This is repeatable, does it every time, PC is dual core quad, Vista, WIFI is state of the art, no problem with bandwith. It did it on 802.11G, and now on 802.11N. It does not do it with any iPhone (including iPhone 4). It also does it regardless of whether I'm running the iPad in Jailbreak or non-jailbreak mode.
When I unplug the iPad, the connection restores. Once again, it DOES NOT do it with the iPhone 4, 3 or 2 connected.