The Gimp is an excellent photo editing program, although it can take some getting used to. It doesn't seem very powerful when you start it, as you only see a small box come up. It's definately worth taking a closer look at though. I swear by it, and I was using photoshop long before the gimp. This might be of some interest to you:
http://gimp-savvy.com/BOOK/
It's a bit dated, but still not bad (and anyway, its free!). Also, photoshop works well with wine. Try this site:
http://frankscorner.org/index.php
Having both photoshop and the gimp running at the same time is great. They both have their strong points and it really gives you a lot of flexibility.
