I've used unetbootin for a friend's Ubuntu installation (worked very well) and tried it with Lenny stable but it didn't work. The second link you provided indicates it is available for squeeze and sid but not Lenny so I assume that's why it doesn't work with the current Lenny stable.
Luckily the instructions in the Debian manual from my original post are spot-on and super easy. Only caveat is to have a machine with an existing installation, although I wonder if a Live CD could handle it? I've used gparted off a Live CD (usb) as a partition manager and it worked great.
Thanks,
Mark