Corporate edition is very expensive because you are paying for licenses for multiple machines. If the corporate edition you are being offered is cheap then I would very carefully check its provenance. There are a lot of knock offs and rip offs of the corporate edition which only become apparent after it has been installed and you try to do any alterations/updates and such like.
I have nine machines with XP Pro all with fully paid up individual licenses. Suggest you get the same, especially if you have only one machine.