I've just done this myself on the driver's side. A mirror is essential I think (As with Brian, a quick raid for a small mirror from the Girl's make up supplies is in order). It was almost impossible to push the little wire clips off as well. I think Halfords were charging £5 to fit it for me and considering how awkward and stressful it was, I kind of wish I'd have paid! Stupid design.
I hope I get rid of the car before it goes on the off side - definitely worth the £5 at Halfords if this goes!
hungry_pete, January 2009