I have had difficulty formatting from the Ubuntu Live Installer when it's a very small screen device. The bottom buttons might not be visible. If this is your problem, too, then you should use the alternate installer ([url]http://www.ubuntu.com/getubuntu/downloadmirrors#alternate[/url]), which is text based.

Also see the Ubuntu installer for Windows ([url]http://www.ubuntu.com/getubuntu/download-wubi[/url]), which is an .exe file to be run from inside Windows.

It sounds like you are attempting to install windows to a partition on your external hard drive that was created with Linux. If that is the case then the problem is with how windows works, windows will only allow the user to install it on the primary hard drive. In most cases when you do a reboot it is best to install windows first then install your chosen linux distro so that windows does not throw fits or overwrite your bootloader.