What exactly is required in order to qualify for the $40 upgrade to Windows 8?

I am planning to install Windows 8 on my machine and I'm wondering what the best way to go about this is based on my rather unusual situation:

My machine originally shipped with (what I understand to be) an OEM copy of Windows Vista Home Premium (32-bit). This was installed on the machine when I bought it - the hard drive contained two partitions: the Vista partition and the recovery partition.

Now, here's where things get a little bit confusing - I eventually swapped out the original hard drive for an SSD and did not preserve the Vista installation (or the recovery partition) on the new drive. I have been dual-booting Ubuntu 12.04 and Windows 8 CP.

Now I would like to install Windows 8 on this machine and I should definitely qualify for the $40 upgrade offer - my only problem is how to go about this, since obviously the installer needs to verify I do have a valid licensed copy of Windows Vista.

There is a little sticker on the bottom of the machine with the Windows logo and a serial number - will that work? I still have the original hard drive with Vista and the recovery partition if necessary. I was wondering if I could clone the recovery partition, dump it on the SSD, perform the recovery to install Vista on the machine, and then upgrade that - but I'd love to hear if there is an easier way.

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Edit: some comments below made me realize that I missed a couple of things in my original question (sorry about that).

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  I have a 32-bit copy of Windows Vista and I would like to end up with a 64-bit copy of Windows 8 (I am using the 64-bit copy of the Consumer Preview right now).

  
  


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  Obviously a direct upgrade from 32-bit Vista to 64-bit Windows 8 isn't going to work. I was hoping to perform a clean installation of Windows 8 regardless of whether I start with my Vista installation or not.

  
  

Answer

Everywhere that mentions the upgrade, at least on paper, indicates that the requirement states that you need to be running a legitimate copy of Windows XP, Vista, or 7 ^[1][2][3], and that you need to have a valid base license and one of the following operating systems. This can be interpreted as requiring that the OS to be upgraded actually be installed (which you can certainly do since you have the key).

However, Microsoft has said

"They won't need to reinstall the previous version to do the upgrade; they can just upgrade on top of the Release Preview,"

So, you should be fine. You should be able to install the upgrade on either your Windows 8 Release Preview or enter your Windows Vista key. The Upgrade Assistant will let you choose to upgrade directly or build installation media. The upgrade process^[4][5][6] will eventually prompt you for a key, and it should detect if the key is from XP, Vista, or 7 and ask you if you want to upgrade. (^{I can’t seem to find the page at the moment—I’ll link to it when I find it—but one of the upgrading to Windows 8 pages specifically mentions that the installation process detects the Windows version from the key, so it should acknowledge the attempt to upgrade.})

Worst-case scenario, you can re-install Vista with your key and upgrade to Windows 8 from there.