newbie questions on PT-015 WALs

I want to get a wide angle lens to go with my Olympus C-5050 and PT-015, but I have a couple of questions.

First off, I keep reading about vignetting. What is it? Is it avoidable?

What considerations do I need to keep in mind when selecting a lens?

Finally, can anyone recommend a good "starter" wide angle lens.

Thanks for your input.

vignetting is where the image edges are darker than the center produced by an optical defect in lenses. its especially prone to zooms at wide setting and wide apatures in my experience.