what version do i want if i want to do the graphics like on peachie.nu (photoshop tutorials) or PSDs?

You could probably use any later version, they aren't really all that different. I think version 5.5 or higher is used by the people who write most turoials, the newest version is 7. If you get any of those you shouldn't have many problems, if any at all.

I'm using version 7, but in the past I've used version 6. It's all basically the same, but the newer versions have some alterations on them.
What version do you have?