Ken, I would decide based on your particular needs, and determine if the later versions' new features are 'must haves' or not.
PS CS for example, has direct features that can handle digital camera RAW formats, has a nice improved File Browser, Match Color command, Shadow/Highlight correction, etc.
Photoshop 4.0 introduced Layers and Actions; Photoshop 5.0 brought us the History Palette and Layer Styles; Photoshop 6.0 introduced Shapes. Photoshop 7.0 brought the new file browser, updated paint engine, and the healing brush and patch tool which are wonderful.
I'm a digital photographer and part-time retoucher; I have
PS CS and could have lived with version 7 awhile longer.
BTW, I don't think you will have any problem following v7 tutorials if you decide to buy CS.
One strategy may be to buy version 7 inexpensively, then upgrade to CS when you feel the need.
Scott