i had 7.10 on the XP drive with 8.04 sharing the Vista drive here. The live install is limited still since you can't add all of the packages available like changing the Gnome or KDE desktops. Being that ubuntu is a smaller distro it's simply more commonly seen in the live cd distribution. In fact the latest 8.10 64bit live cd is still sitting in the cd drive here presently waiting for the next boot from that.
strker16 seems to be wondering about how to get Linux as the main OS on an older system lacking one presently where he will want a full OS with all options supported. A live install is a quicky for those that simply what to dual boot without fuss there. The newer releases of Zenwalk, Knoppix, and others have been made easier to install and use as well.
Downloading any ISO disk image and not being able to burn it to disk either lacking a cd writer or dvd burner or a program that will work with iso type images is another problem besides choosing which one. A rather recent free program called Starburn will effectively burn the unbuntu or other distro's iso image in order to first see either the live cd or bootable install only type disk(s) made up.
http://www.rocketdivision.com/download_starburn.html