Good starter is Photoshop Elements, its like light versio of "real" Photoshop, Elements cant do all tricks but i was pleased with it when i tried that (2.0 came with my camera), i think current is Elements 4.0 and costs way below $100 i think.
If you want full Photoshop, you only need that part of it, there is full Creativity Suite packages that do cost arm and leg ($1500 or more) and has nearly all Adobe products, i do have Photoshop CS2 right now... and comes with 2 extra softwares like Bridge that is picture manager etc and ImageReady that allows you to make animated gifs for example... sure even that costs like... $700. prices really do vary alot, in here that Photoshop CS2 can have $400 price difference
I really, really want to respond with an answer that most know is coming.
However, I recently did have to *legally* aquire Photoshop... for my girlfreind... whom is a graphic artist - she can't simply use the 'same' version I do and she did anymore, not while selling her work, at least.
This one is up to the moderators/admin... should I help the poor guy out?
does virtually everything Photoshop does, and it's free (open source). It can hold you over until you're ready to fork over the cash for Photoshop.
If you're still in school, you might be able to get an educational discount on the software. My school offered the full Adobe creative suite for $200 as a special students-only deal.
I use Photoshop 6, which works fine for me even though it's a few years old. If you just want to play around, look for one of the older versions. Might be cheaper than buying the newest release. Plus you can always purchase upgrade packs later for a crapload less.