An OEM Key will not work with a Retail Disk.
A Retail Key will not work with an OEM disk.
A 32 bit key will work on a 64 bit disk if it is the same type (OEM key only works with OEM Disk, Retail Key only works with Retail disk, and I know from personal experience a SP1 Retail Key will not work with a pre SP1 disk).
Error 10 had a link on how to get a OEM 64 bit disk somehow.
edit: HERE it is, $30
However, you may have run into OEM discs that were modified by the OEM. Dell does this to automate the installation process so users don't have to choose a Vista edition or type in the product key, and other OEMs may have done similar things. They do this by using the built-in automated installation tools that come with Vista that also allow corporations to make standard install discs. If you had used one of those discs on a non-Dell system, then you would have activation issues. It is possible to modify those discs to remove this behavior and get back to a mostly clean disc.
After looking at the link to the other thread you posted, I can see how that might be the source of some of this confusion. If you go to the MS site to try to order the replacement disc, it will not accept an OEM key. That is because MS doesn't support OEM editions, and not because the key would not work if you were to try to install with it.