I tried krita for a (short) while, and found it pretty good indeed (from the little I used it, at least on par with PS for drawing), but got incredibly frustrated when It crashed everytime I tried to rotate a canvas, despite my PC not being that old and crappy. Perhaps that's solved with the newest version though, I'll get back to it
regarding PS CS2: it works, obviously doesn't have all the newest stuff, but does have some I didn't think were already there. It installed ImageReady without asking (and I don't know what that's for) however...
If you still have a PC with windows XP (like me until monday
), then you should probably get Photoshop CS2 rather than a newer, probably unsupported program. However if you have anything more recent, go for the recent things of course, you'll be sure they won't crash your computer