Adobe Photoshop CS Upgrade

[lom8104]

I have the Photoshop CS upgrade and am now looking to purchase a photoshop 4.0 license so that I can use my upgrade.

Do I need the Mac version or can I upgrade from the PC version?

Does anyone know a good place to purchase 4.0? Is there a way to verify that the license I purchased is valid? I am concerned that if I bought one off of eBay I would not be able to validate it with Adobe (I beleive I have to call in the registration with CS)

 

[lom8104]

Anyone?

 

[CanadaRAM]

I have the Photoshop CS upgrade and am now looking to purchase a photoshop 4.0 license so that I can use my upgrade.

Do I need the Mac version or can I upgrade from the PC version?

Does anyone know a good place to purchase 4.0? Is there a way to verify that the license I purchased is valid? I am concerned that if I bought one off of eBay I would not be able to validate it with Adobe (I beleive I have to call in the registration with CS)

The upgrades are not cross-platform as far as I know
http://store.adobe.com/store/products/master.jhtml?id=catPhotoshopUpgrade
"To install this upgrade successfully, you will need a licensed version of any version of Adobe Photoshop, on the same platform as this purchase."

Also there is an excellent chance that the previous owner of software sold on eBay had used their serial number for an upgrade already.