Hi, I haven't checked it but I may be installed on USB. I installed ubuntu and other live distro from usb , by using unetbootin.
So if you use inetbootin to install the iso ( regular CD1 iso) to usb, then reboot from the usb and you can install on hard disk thru this usb. We must to check it. I have installed debian and other ubuntu on usb hard disk, (extern HD), and I can reboot fron the usd HD, even the PC doesn't contain any linux system. It is a good idea to have a system on an extern HD, you can run linux on machine running just window$ for example, by booting from your HD. best regards abd bela.