Formatting and installing Windows 7 using an upgrade disc

Evil Multifarious

Here's my situation:

-I had a genuine copy of Windows XP installed 3 years ago or so.
-I bought a digital upgrade copy of Windows 7 Home Premium, 32-bit, and installed it over Windows XP
-I want to format and reinstall Windows 7, but now that I have more RAM and a 64-bit processor, I want to install a 64-bit copy of Windows 7.

So, my questions are:

1) Will the key I have from my upgrade copy of Windows 7 work when I activate a 64-bit Windows 7 install?
2) Will the upgrade disc I burned 3 years ago be able to install a 64-bit version instead of a 32-bit version? I'm guessing it won't since I had to choose before purchasing, if I recall correctly.
3) If not, but my key will work, what's the best way to get the software to install without actually buying it, since I already have a key?
4) If I do end up installing Windows 7 from the upgrade disc, how can I ensure I don't get the notorious "this key is only for upgrades" error, since I know it's totally possible to do a clean install with an upgrade disc in some circumstances?

Honk

I got Windows 7 through digital download and there were different files for 32 and 64 bit versions, so probably your disc won't install W7 64.

Dehumanized

1) Yep, your key will work fine. Windows 7 keys are interchangeable between x64 and x86.
2) Nope, you'll need 64-bit install media.
3) The easiest way would be to find a friend with 64-bit install media* and use theirs. The harder way would be to contact Microsoft support and ask them for 64-bit media. If you're lucky they'll provide you with a digital download, if you're unlucky you'll have to purchase physical media from them... which will probably run around $10-15 and take a week or two to ship. Since you've got a license key, they will work with you.
4) You'll be asked to enter your Windows XP key as you install. If you don't have it anymore, just install Windows 7 (and don't bother entering your license key, it gives you a 30-day grace period to activate) then install Windows 7 again over your existing install. You'll avoid the upgrade key check that way, and as long as you own licenses it doesn't matter how you get it installed, from a EULA perspective.

*If their install media does not match your version of W7 (such as they have a Windows 7 Ultimate disc), then it is possible to prepare new install media based off theirs that will be version-agnostic. This link should help, should it come to that: http://code.kliu.org/misc/winisoutils/

Evil Multifarious

That's excellent, thanks for the info! I think I can get my hands on a Win 64 disc, actually, of the same edition, and if my key works then I'm set. I even have my old Windows XP key as well, in case I need that.