There is no such thing as a "corporate" version. That's a term used by the
pirates for the illegal Volume Licence version which was spread when XP was
released. If you're PC came with XP preinstalled, then it's an OEM, if you
bought it with a piece of hardware and it wasn't in a nice box, then it's
OEM. If you bought it on it's own and it's in a nice box, it's a retail.
If you work for a large company, then it's probably a VLK (Volume Licence
Key) version...