like i said in #3 get yourself 2 wireless cards pci or usb , set them to ad-hoc made, stuff a long rj45 cable into the xp machine and use that as the master machine.
or goto your local hardware shop and ask for parts to extend your cable, some cable coax, 2 screw on connectors [the same as the one connected to your stb] and a female to female [or is it male i forget?]
adaptor to join it all together and move the CM into the same room as the xp machine , about £4.
you never need to mess about with powering down,repluging,powering up etc,etc.
you can always pull these cards as you upgrade your machines and usb2 wireless makes it so easy to do.
http://www.allcomputers.co.uk/prodcat.asp?CatID=15
£13.19 Mercury Wireless G USB Adapter
Wireless
or get the cheaper 11g pci cards if you like, dead easy to install into a spare pci slot,install a driver and a wireless client app (if you dont use the xp installed app), run the wireless networking setup in control panel and away you go, done......