Windows 2003 activation nightmare, changed hardware

Solution 1:

The only way I know of to change the product key from OEM to VLK is to do a repair install. This is a risky thing to do on a production server though and I don't recommend it. I have had success in the past running a repair install from volume license media and then using a volume license key.

Solution 2:

You can't use a VL key on a retail/OEM product.

Their licensing is completely different, and they even have different install media. This is not only a licensing restriction, it's actually impossible to do from a technical standpoint (unless you want to manually replace DLLs and so on).