One of my Ubuntu ninjas wrote me this morning to point out that the mechanism behind the Wubi installer for Ubuntu (http://wubi-installer.org/) is being incorporated into the next version of Ubuntu (7.10 aka Gutsy Gibbon; due out in just over a month).
From the Wubi web site (say that ten times fast!):
Wubi is an unofficial Ubuntu installer for Windows users that will bring you into the Linux world with a single click. Wubi allows you to install and uninstall Ubuntu as any other application. If you heard about Linux and Ubuntu, if you wanted to try them but you were afraid, this is for you.
Not too shabby, no?
The Ubuntu archives have some of the notes on this, and I suggest you check them out if you’re in the dark on this one.