"This article by Christer Edwards outlines the steps
required to install and run the latest previews of GNOME Shell,
which will become GNOME 3.0. The final release isn't scheduled
until later this year, but there are preview snapshots available
for testing and feedback. Installation of GNOME Shell can be done
alongside your normal installation, so you don't need to worry
about it interfering with your "regular" desktop.
"Remember, these are development builds and preview snapshots,
and are still in the early stages. While it appears to be
functional (so far) your mileage may vary.
"With the release of Ubuntu 9.10, a GNOME-Shell preview is
included in the repositories. This makes it very easy to install
(and remove) as needed. The downside is that it is just a snapshot
so you are not running the latest-greatest builds. For this reason
I've included instructions on installing the package as well as
compiling the latest builds.
"I should also note that GNOME Shell requires reasonable 3D
support. This means that it will likely *not* work within a virtual
machine. In particular, problems have been reported trying to run
GNOME Shell with 3D support in VirtualBox."