Worth the time to download and learn to use?
Photoshop is one of the greatest single programs ever created (imo). I’ve been using it for 15 years and probably know of or use about 10% of its capabilities.
Yes. Even if you only use it just to retouch photos you'll have fun with it. Plus there are endless free tutorials on the web for specific tasks you may want to perform.
It depends on whether you are a professional or a tinkerer like me. CS2 is very powerful. I purchased it years ago and have used it extensively as an amateur photographer since then. I still have not found a good reason to pay the price for a newer version. I use it in conjunction with Adobe Lightroom 2 and am quite satisfied. I recommend Scott Kelby’s book on CS2 to learn how to navigate the user interface. It is much quicker than trial and error.
I have Photoshop 7.0, I am assuming CS 2 is a more feature robust version.
There is nothing better than PS for digital editing. Lot’s of tutorials on the web to get you started too.
Go for it!!