I would say if you have Photoshop CS, look into CS2 or see if you can downgrade to 7. A lot of things were added to CS that slow it down and make it a virtual boat anchor, and they were either cleared up in CS2 or never a problem in 7 in the first place.
I have Photoshop 7 and CS, and definately prefer 7 (I keep CS around so I can convert brushes, because I am a HUGE brush fan).
Comparing Photoshop and Illustrator, they really are two different things. Illustrator is great for vector stuff, but Photoshop is wonderful for manips and raster. I love Photoshop, but I tried poking around in Illustrator and got a little confuzzled. Consequently I ended up poking around Freehand for comparison, and I might end up trying to learn that instead.