I personally really like Photoshop and Paint Shop Pro. I tried the Gimp, but when I tried it, they still didn't have all the bugs out.
There are a wealth of tutorials on the internet that can help you do some stuff, but they are complicated usually and it is good to get the hang of the program first. http://eye.box.sk/box.php3?noup=yes&gfx=eye&prj=eye&key=tut&txt=tutorials,%20manuals
That is eye.box.sk's list of tutorial links. Check it out.