Two computers on the same connection is what is eating up your bandwidth and causing a high ping rate Nut.
I have the same problem here with my router and a home wireless network consisting of my PC, three lap tops and occasionally a PSP connecting. Before I play online I announce loudly to the rest of the house I am about to play and if anyone lags my connection I will publicly execute them.
Works for me every time.
Yo, Slaine! Would this effect console gaming as well? For example, in my household, I have a desktop hooked to my wireless router, and my PS3 hardwired into the wireless router. Would downloading content onto the desktop slow my PS3 connection and cause interruptions? If my wife joined the network via her laptop to the wireless router, would that slow the connection to the PS3?