Thanks Stick,
Seems a bit dopey that the only way you can get this info is when you click the order button.
It would appear that you'll be able to upgrade the individual products as follows "All software upgrades require you to enter the serial number of an earlier version, on the same platform as that being purchased, during the installation process" This is good news as I intend to upgrade to Photoshop CS but never upgraded from 6 to 7 as I didn't feel it was a valid upgrade.
feel the heat.