There is a file (ei.cfg) that you can delete from the ISO and resave the ISO
AS I understand it (have not done it) you should then be prompted for which version of windows you want to install
But as I understand it also, there won't be any choices like Vista install.
Each disk is different like XP isntalls, but all versions are still on disk for the anytime upgrade feature.
People were too confused on how to install Vista with too many choices.
In the final version, as in Vista, you are asked to choose which version to install. Towards the end of the install (Yes - that has now changed) you are asked to insert your DVD code. This is the deciding factor, as you must have the correct code according to what you have purchased, and therefore chosen to install, or it will state it is invalid..
Added. To clarify, I should have added, this will not, at this stage, prevent the desktop from opening. You will be in the same situations as with Vista. 30 days to licence the product or lose functionality after that time.