Ubuntu Linux 8.10 release candidate beta version has been released and available for download from mirrors. The final stable version will be released on October 30th, 2008. But, if you would like to test latest version try out Intrepid Ibex RC beta version.
You can install latest Ubuntu Linux 8.04 under Windows Vista / XP without creating a new parition with a new tool called Wubi. It is a Ubuntu installer for Windows users that will bring you into the Linux world with a single click.