I finally got to try out goodbye-microsoft.com this past weekend. It uses similar principles as UNetbootin, which Utumno recently wrote about. I had a donated machine in a computer lab i volunteer at with a flakey CD-ROM which i couldn't get to netboot. Since it had Windows already on it, i booted to Windows, hooked into the network, downloaded a debian installer for Windows, ran it, and was on my way.
The project is clean, simply done, and provides a good interface in the leadup to rebooting into a debian installer. I highly recommend it for folks who need to switch a 'doze machine to the One True OS.
My one concern with this approach is if the debian install fails midway through, (and you haven't done any gymnastics to preserve a dual-boot scenario) you could be left with an unbootable machine. But the debian installer is pretty much rock solid these days, especially with common commodity hardware, so you'd probably have to trip over the power cord to get caught out like that.