surely you can do this through your router Bubb's?
Blocking US IPs? Harder than you'd think.
You have to obtain all the US IP address ranges, then feed them into some sort of blocking software. You also have to make sure that you don't block the XBL IP addresses for obvious reasons.
I can't remember the best place to find US IP address ranges now, they are published somewhere. They change often so you need to keep on top of it.
If it was one continuous IP range then it'd be easy to do in the router but it's not, there's hundreds of them. It'd be a pain! Also, it kills surfing to any US websites so you want it to be as easy as possible to turn on/off.
The software I used was
Outpost Firewall along with a free plugin called
Protowall which could accept the IP ranges. There used to be a whole Halo 2 community called "wallwalkers" (after the effect of walking into walls under extreme lag) dedicated to updating these ranges. They've gone now though.
It's quite likely that the current XBL would detect this sort of thing and ban you, though I'm not sure if they are technically allowed to do that for using a firewall.