Question about windows 7 upgrade

[Neb]

So I am building a new computer that will have no OS. I can get the Windows 7 upgrade disk for $65. And if I understand correct I will not be able to just install that as my OS because there is nothing there to upgrade. But would it be possible to boot it from a windows vista free trial and upgrade that to windows 7? Otherwise I'm out $200 for the full edition.