I'd stick with Photoshop elements 7 if I were you. Like everyone says it almost does everything you want it to do. I had Photoshop CS2 when it came out and it was nice but it was difficult to learn.
I have right now Photoshop Elements 6 and I love it. I have Corel PSP x2 and the pro (on different computers). i also have paint.net (which is free to download). If you're not a student and can afford to spend the $500+ it costs for Photoshop CS4 then get it.
I don't have alot of time to edit photos. I just mess with the curves and do some cloning and that's about it.
I did a search for what you wanted to do, here's the link...
Adobe Photoshop Duotones
Go to youtube and do a search for tutorials, there are a ton of them. If you learn to do actions or want to download brushes or fonts or whatever deviantart.com is a good website for those things