This comes from the MVP RSS feed, so i've directly linked to the publishers blog, Stefan Krueger links to an article (by the Wndows Vista Blog team) about Vista's UAC dialog prompts.

Whats interesting is that it gives you an insight in to how Vista manages UAC interactions with the user, and provides a method for automating these UAC interactions.

And here is a link to a Microsoft document on describing UAC in detail.