Re-install same Win 7 DVD/serial number on a flash drive?

[x509]

If my system is already running a fully licensed version of Win 7, can I use that same install DVD, with the same serial number, to install Win 7 on a USB flash drive? .... or a USB-connected external hard drive? ... or a SATA-connected external hard drive?

If yes, what happens if I use that USB drive on a different system? Will I somehow raise flags in Redmond?

 

[Bahamut]

The Product Key will only be valid on one activated machine at a time, at least that's the general theory. I've heard and read people make comments about using the same key on several installations at the same time and each one has activated - and I'm talking about standard Retail-class Product Keys here - but I've yet to actually see such activity in real-life. The basic idea is that since Microsoft tracks the keys and the activations, as soon as any given key is used for a potential activation a second time it'll choke and won't pass, but go right ahead and make the attempt if you wish.

Windows 7 won't work off a USB Flash-drive meaning installed to it like it was some actual working drive (you can install from such Flash-media devices, just not to them), and afaik it won't work off anything USB-attached - SATA or eSATA sure, but USB, ain't happening. If you can get it working that way more power to you I suppose, but it's not Linux so it's not really designed to operate in such a manner even in spite of the improvements made to it over the years.

Windows isn't a portable OS as Linux can be with hardware detection and driver choice being done literally on every reboot on new hardware. Windows is designed as a static OS, with the overall hardware detection done during the installation and secondary detection done on each boot to compare it to the previous successful boot process. It's just not a "portable" OS like Linux can be or is...

But go right ahead and experiment so you'll get the proof you need firsthand.