Amy, there is so much to learn from using Adobe Photoshop it is scary. It is almost a lifetime excursion to get even partially proficient. I have been using it since the late 90s and still only scratch the surface of it's capabilities. I am only a personal and learning user and have been since Photoshops 5 version.
I had Photoshop Elements 6 which was a step to start learning the elements of things the Photoshop versions can do as well as combining graphics with photos. The later versions are much better I suspect. For photography only, there are easier packages to learn as mentioned in this thread. Just learning to do conversions well from raw to usable print outs or web displays is a journey in itself. ACR for Photoshop is awesome as other vendors raw converters are I am sure, but once you learn how to work in Raw Formats and making useable outputs, personal photography takes another step upward for most people. At least it did for me.
Trust me though, to learn Photoshop CS-4 or CS-5 to any degree of proficency takes many many hours of self indulgence in the medium of art, design, and video creations. I have CS-4 extended and just recently learned how to make animated gif files which are neat to do from photographs. That learning step took me a long time to master. If you commit to a full version Photoshop, you will never regret it if you immerse yourself into that as deeply as some do. And basic creation steps once learned allow newer processes to be absorbed more quickly. I just figured out last evening how to make brushes and did some from photos..neat stuff. It is absolutly phenominal what you can do by combining the two crafts of Photography and Graphics.
I bought the first Photoshop as a Academic purchase since my wife was a school teacher and then kept upgrading ever other version since. This happens frequently and is a significant savings over time I suppose. CS-4 was the really first good version for me to use and learn to gain momentum in how it works. I use Windows but it works with Macs or Windows really well. Also there is plenty of help for Photoshop on the internet or forums and the Photoshop Help built into Adobe's site is pretty good too.
Did not mean to be so wordy here, but to really learn Photoshop and Photography has to almost be a passion to excel in those mediums. And lots of spare time. Here is a pic of a Photoshop creation I did from a brush I made that was from a photo of a wooden mouse I made from wood in my other hobby..woodworking.... Good luck in your quest.
Mike T.
Hope the pic shows up as I have not tried this before. This was a practice to play with newly made brush.