A set doesn't need to have the HD ready badge to support HD signals, the best HD plasma you can buy doesn't earn the HD Ready logo in its bog standard form.
You'll be fine with a monitor, theres no way they'd take out 4:3 support. The horizontal resolution would be decreased to make it fit but you'd basically be getting 4:3 HD, I think thats pretty much exactly why they're releasing the VGA cable, so that people can use monitors for HD.