How do you change the document icons?

I changed the default programs for opening various documents, but they still
kept showing the same icons in explorer. For example, I don't use WordPad
for RTF documents, but the icon on each document is still the old WordPad
icon. How can I change the icons when I change the program that opens the
file? This used to be easy on Xp, but I seem to be overlooking something in
Vista.

Thanks for any help.