[CentOS] yum problem

Hi, all.

I'm experiencing a problem with Yum. When I call 'sudo yum update' it 
tells me that it can't find any mirrors & after doing a 'sudo yum clean 
all' it just informs me it can't find any base repo & quits.

This is on a brand new installation of CentOS 6.2 x86_64. I suffered the 
same problem with Fedora 19 too.

I have several Ubuntu & Mac OS X machines that suffer no network 
connection problems & I can connect to the InterWeb just fine (via two 
HP Procurve 2426s).

Any help appreciated.

Cheers,

      Phil...