>Is this possible today?
>
>I'd like to sync my computer to a USB hard disk, attach it to another computer and painlessly boot up in my same environment somewhere else. I't be great for traveling.

There are various utilities available that let you copy partitions from one hard drive to another. That would "sync" your local HD to the USB drive.

On the other end you'd have a couple of issues:

1. The other computer must support booting from a USB device in its BIOS (typically only fairly new computers support this)

2. As Viv points out it may not boot properly, or at all, if the hardware is significantly different. A couple of times I've done this sort of thing and I've been surprised at how effectively Windows "detects new hardware" and reconfigures itself for the new hardware. The big issue would be if your Windows installation didn't have all the drivers for the new system, you'd have to supply them somehow, either from the Windows installation media or from download to a separate machine etc.

3. Also as Viv points out, if you're using XP and the hardware changes significantly that will invoke MS's copy protection/activation requirements.

This is why people buy laptop computers :)