[CentOS] INSTALLING UPDATES-PROXY PROBLEM

Dear all

I have centos 6.0 in my system and i want to update packages, so i tried the yum commands for checking and installing updates, but my proxy is objecting and i got the following error

Loaded plugins: fastestmirror, refresh-packagekit Loading mirror speeds from cached hostfile Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=6&arch=i386&repo=os error was 14: PYCURL ERROR 22 - "The requested URL returned error: 407" Error: Cannot find a valid baseurl for repo: base

i tried with the software update GUI in centos 6.0 but still the same proxy problem....can any one please suggest how to overcome this problem and install updates for packages.

Thanking you.

Regards