Dual booting multiple Linux OS from External Hard Drive
I'm still fairly new to linux (started testing around with it about 6 months ago), and I want to have multiple linux os's boot of a 500gb external usb hard drive. The os's I have in mind are Ubuntu, Lubuntu, Arch, Puppy Linux, SUSE, Fedora, some sort of SliTaz, and anything else that sounds interesting as I learn more about linux. I have been able to install Ubuntu 11.10 using only 100gb of the hard drive. I created a main partition and a linux-swap partition. I tried to now also install lubuntu alongside it on a seperate partition and it seemed to work, because I went through the installation process and finished it. When I boot from the hard drive it just automatically starts Ubuntu. How can I make the computer give me a choice for which OS i want to run. I have heard that something called GRUB can do this, but I have no idea how to install, use, or what it really is. Please help.