Well, I personally make all my stuff in Photoshop, so if you don't have that, that's a bit of a bummer.
But! One of my friends doesn't have Photoshop either, and she still makes some icons herself by using this website:
http://www.picnik.com/
Just choose the photo you want to make an icon of, follow their instructions to upload it, and then use their tools to crop it to a square and resize it to 100x100 (for LiveJournal sized) or 150x150 (for using here) and add some of their Creative Tools to your icon to jazz it up if they look good. Pretty easy to use, and it doesn't require any software on your computer.
You can use the same method to make simple signatures, and even wallpapers!
Hope that helps a little!