[CentOS] Installing xfce on CentOS 5.3?

I would like to install xfce from the "extras" repo - but when I run:

  yum groupinstall XFCE-4.4

I get:

Warning: Group XFCE-4.4 does not exist.

Also 'yum grouplist' appears to only show the base groups ...

Is there anything else I have to do to install xfce?

Thanks

James Pearson