GIMP is fantastic, but it's interface is what I would call a mac-users biggest nightmare haha.
Jaymz, if you want to take things to a professional looking level, it's best to dive into Photoshop or GIMP really. It ain't that hard. Your first projects will look like shit, but after a short while things will eventually take shape... it's not magic and there are tons of noob-tutorials on the web that will have you flying asap.