Using key to choose version?

[gospeed]

After using the Vista Anytime DVD, I like how, by typing in your key, IT chooses which version to install. Has anyone developed a way, where inside the boot menu, you could type in your key and it would decide which version, and chain it? I am not sure how that would work with the winnt.sif, it would be nice to only type the key once. I have searched and cannot find anyone that has done this.