I think that there is a lack of understanding about high definition content here.
The problem is not that the product hasn't been done, the problem is, using current hardware, it CAN'T be done. Even 720p content, which is 1280x720x60fps requires so much bandwidth your motherboard, let alone a USB port, couldn't keep up. You have to understand, this is not video that you download off of the internet, but uncompressed, raw, analog video clocking in at 1.1 Gbps (http://www.cedmagazine.com/article/CA6261143.html)
. That simply isn't possible.
The only alternative would be using firewire. This has been done using Motorola cable boxes, hacked drivers, and some software. This can be done because the boxes will pass the mpeg-2 compressed video over firewire before it is decompressed, allowing the PC to do that work yet still allow you to view the picture in real time. The XBOX 360 obviously doesn't have firewire, so no go there.
Sorry fellas, looks like you are stuck. This has been discussed in serious length over at AVSFORUMS.com. The only alternative is a cheap CRT monitor and RGB cables for the 360.
EDIT: On second thought, another alternative would be to mod the screen input to accept DVI-input. That would work with a PS3. I don't think the 360 has a DVI cable available.