Can I determine the product from just the key?

This may sound a bit strange, but I have a old Windows CD-key and want to know whether I can utilize it on a virtual machine or if I should just toss it.

I am reasonably sure that it’s from an early Win XP, but I cannot be 100% positive, because I just tried to use it with an install of XP Pro (32-bit) 2002 and it was rejected.

I no longer have the original coa tag, just the key, hand-written on an index card.
Nor do I absolutely need it… I just hate throwing away anything I spent money on, if there’s still some way to put it to use.

If I could determine precisely which version of Windows this keep belongs to, I can easily come up with a CD for it.

Here’s hoping someone will be able to assist. = )