Command line to install additionnal softs

Hi,
Could someone give me any piece of advice about how to know the 'real' name of a package to be installed.
For example I wanted to install XFCE as Desktop Manager. So I tried urpmi xfce4, urpmi xfce... but none of these were the right name, I had to look at xfce.org to find out the name of the main package to install.
Is there any way to find out easily the names to be used to install the needed softwares ?
Thanks
Could someone give me any piece of advice about how to know the 'real' name of a package to be installed.
For example I wanted to install XFCE as Desktop Manager. So I tried urpmi xfce4, urpmi xfce... but none of these were the right name, I had to look at xfce.org to find out the name of the main package to install.
Is there any way to find out easily the names to be used to install the needed softwares ?
Thanks