Centos 5,3 and yum

[Centos_user]

Hello Guys,
i got lately my host installed and configurated runing Vmware server 2.0.2
the only problem i have now is i am behind proxy so my yum is not working,
i did all the solution i can find in google
edite the etc/yum.conf file and /etc/profil
adding the proxy, export the proxy but nothing help
when i run yum update i get the next error and hope someone can help me with this

l-linuxtest /]# yum update
Could not retrieve mirrorlist http://mirrorlist.centos.org/?releas...64&repo=addons error was
[Errno 4] IOError: <urlopen error (-3, 'Temporary failure in name resolution')>
Error: Cannot retrieve repository metadata (repomd.xml) for repository: addons. Please verify its path and try again