Well, if you want to do it yourself, that's great!
You can use Photoshop to "extract" images that you have. Use the extract tool (and for the life of me I can't remember what the name of the option it's under - its on the right side somewhere)!
After that, you need some sort of background. You can use regular colors or whatever, but Photoshop has the ability to make virtually any shape or effect you can think of! I normally go to a "tutorial" site such as http://www.good-tutorials.com
to find something I like and then duplicate it myself.
For an av, make sure the size is 80 pixels square or less. You can use the "image size" tool to shrink it down. I think it's under the "Edit" bar, but once again, I don't actually look at what bar it's under when I go there! Signatures can be bigger, but only 10k in size. You need to use the "save for web" option (under file - haha!) and optimize the sig until it's under 10k.
I just tried to do a bunch of stuff with tutorials when I got the program...the only way to learn is to just try things and see if they work! You'll exponentially increase the quality of your artwork if you do. Good luck!