Found my old copy of Photoshop 4.0 and the manual, so I decided to go ahead and get the CS (MAC) upgrade. It was late at night and I was impatient, so I decided to buy the download version direct from adobe (Thank God for 3 meg Cable!). The old version was not installed on my machine. I was expecting the upgrade to ask for my old serial number. It never did!!! I received an e-mail from Adobe as the upgrade was downloading with a new serial number. It was like I bought a full new package. I thought Adobe was a lot stricter about this stuff. I do have Elements installed on this machine, but Adobe states explicitly that elements is not eligible for the upgrade. PS-the lady at the Apple Store emphatically stated that the CS upgrade only worked on 5.0 or later, but Adobe's site said "any previous version" so I rolled the dice.