Dig into Fedora 7
This month I had a chance to install and test Fedora 7, the latest community-based release from the folks at Red Hat. Fedora and Novell's OpenSuse are Ubuntu Linux's two chief "competitors," if you care to frame things that way. All three distros are free downloads; all have vibrant online communities where you can go for tips, troubleshooting, and advice; and all three will hook you up with a modern, friendly environment that you can start exploring right away. If you don't rely much on proprietary, Windows-only applications, you may be able to get to work right away, too.
The Big Three Free Linuxes differ mainly in their focus. Fedora and OpenSuse both serve as proving grounds for new technologies and new approaches; you see new features and capabilities in these distros long before the features and capabilities appear in Red Hat Enterprise Linux and Suse Linux Enterprise. So Fedora and OpenSuse both do a good job of evolving -- and that suits the companies that fund and steer these projects, as their commercial products directly benefit from the evolution.