|Gnome3 screenshot in OpenSuse 11.4|
1. By adding a URL to the repository list.
(which is this - http://download.opensuse.org/repositories/home:fcrozat:gnome3/openSUSE_11.4)... then perform an upgrade.
However, there seems to be few issues with that (haven't happened to everyone but for some it seems). So the best option is to..
2. Download Gnome3 live CD that runs in OpenSuse directly from Gnome3 official link and do a fresh install rather than going for an upgrade (not sure even if you can upgrade from that Live-CD - sorry I'm not an OpenSuse user... used to be, great distro btw ).
If you want additional information... then please read this thread.
Update (April, 13) :- According to a recent OpenSuse blog post, within the next 2-3 days they'll provide an official Gnome3 repository. If you want you can add the repository in your Package-manager, which would automatically notify you when the updates are released.
If interested, here is the official repository = http://download.opensuse.org/repositories/GNOME:/STABLE:/
But remember, at the moment, still they haven't released it yet... but it should hit the downloads within next 2-3 days... so hang on there! :).