Yes you can download your Windows 7 ISO from whereever you want, I personally always download a modified Windows 7 Version with all updates and Service Packs integrated.
As I.M.O.G. stated this is not intended by microsoft on the other did I pay for this product and feel free to use it the way I want. I could download Win 7 from MS and modify it myself but why would I do that if others already did that for me.
The keys activate 32bit and 64bit as well, doesn't make any difference. It is just important to use the correct version of windows with your key.
I think OEM keys are locked to the hardware it was first installed on anyway, at least the MS Supporter told me so when I lost my key for my laptop.
Thanks for the help on the 32bit/64bit, I wasn't sure on that.
However on the downloading from wherever you want part, technically that isn't accurate. You may feel it is your right, however the EULA that governs your rights by your purchase states otherwise. So technically, we aren't free to use it any way we want. Thats what is cooler about Linux than Windows, and its an advantage open source has which closed source software does not.
Others also commonly download versions and use legitimate keys, so its not that its uncommon, just that we can't recommend doing so. There are legitimate risks, especially if you do not know the group who created the release, and even more so if you go through torrents where there is no way to verify if the release actually came from that group, or if its a re-release by someone who dropped trojans or other malware. A lot of these downloads are infected, as its an easy way to get crap on people's machines who don't know how to filter out the safe warez from the dangerous warez... The aXXo releases are an especially good example of this. When his popularity peaked, tons of downloads were labeled as aXXo that were not legitimate, and many of the illegitimate ones were bugged. The legality, as well as those risks, are why we don't encourage any warez stuff.
I get what you are saying, I just wanted to address that part because our rules about downloading copyrighted stuff are pretty strict, and we have to have a clear position, so that we don't get bothered with DMCA notices.