Coaxing Off-the-shelf Generic PC into Pristine Win 7 Pro

A lot of generic off-the-shelf PCs don't come with Win 7 install media. Some don't have any restore media at all (relying on hidden hard drive partitions) or have install media that restores the machine to factory conditions. The "factory conditions" just reinstall 3rd-party demos and other "cruft" that buyers don't really want.

I need a PC that has only Windows 7 Pro on it and nothing else.

I'm thinking of just buying a Win 7 Home Premium machine off-the-shelf and also a Win 7 Professional upgrade disk. Then, use the Win 7 Pro upgrade DVD to nuke and pave the machine like I want it.

Will this plan work? Will a Win 7 Pro upgrade DVD permit this?

If not, what is the best course to take in order to get a generic PC into a pristine Windows-only state (under constrained budget circumstances)?

I'm afraid the upgrade disk will leave any baggage in place. The only way to achieve what you are seeking to do is to make a clean install of Windows. This would involve reformatting the drive and eliminating the Windows which you had already paid for in the purchase price. Best way to avoid all of this would be to build your own machine although a number of manufacturers (such as Dell are now offering machines for sale with no operating system installed.