Not all disks have all versions on it.  Some disks will let you choose, some will not - but you are asked before entering your Product Key IF you are asked at all.  If you ultimately want to upgrade to 7 Ultimate and only have a Home  Premium DVD, then you must first upgrade to 7 Home Premium, Activate it using a Home Premium key, then do an Anytime Upgrade to 7 Ultimate using the key you have.
I have a Windows 7 Premium DVD disc and a Windows 7 Ultumate Key, I was told that the key you enter would determined the version that would be installed. Does anyone know if this is correct? I was thinking that i would need a copy of Windows 7 Ultimate DVD. I am trying to upgrade my desktop from Vista to Win. 7 Ultimate. Thanks for any advice on this.                                                                                                                                                                                                                                                Thanks,                                                                                                                                                                                                                                                William
Windows Ultimate Product Key