"Speed (Downstream/Upstream)1 Uncapped/128"
WTF no DSL company's are going around with uncapped services, unless this is just a marketing saying they dont limit that 8 meg of service, but most people will not get that 8 meg due to australia's crappy artechtechture.
Try a speedtest. http://www.broadbandreports.com/stest
Now to me this problem seems like bandwidth priority problems. The XBOX doesnt use much and the router knows that. Theirfor it will give the PC much more bandwidth to download things, as a 200 or so ping is not bad for downloading stuff really.
I have the same issues, their's some software to limit what your computer to use. I have a cisco router and even have this problem, and It's too cheap of a cisco to assign a percentage to the ports