Personally I use Paint.net in conjunction with GIMP using GIMP to create .GIF images. I'm not too good at picture editing myself but I would recommend using Paint.NET and GIMP together even if they had the same functions
Alternative? Hmm....well there is Artweaver. It's a freeware thats a clone of photoshop, and its free and easy to learn to use.
http://www.artweaver.de/index.php?en_version
oddly no one have suggested this yet... but there exist a lightweight version of photoshop online, which is free.
I have not personally used it, but I have read lots of good reviews of it, so maybe you could give it a try? :)
I mostly use Gimp but photoscape is good for basic to moderate editing you can download it here.
http://download.cnet.com/PhotoScape/3000-2192_4-10703122.html?tag=mncol