Without joining hte mac vs pc battle...

If you have a mac, and want a RAW editor, either Aperture 3 or Lightroom 2.

for PC, Lightroom 2 hands down. Please note this is for a RAW editor.

For general photo stuff, a newish to top version of photoshop will do you fine, but it takes a while to learn things, but there are a great number of tutorials out there.