install xtables-addons in proxmox

I wanted to install xtables-addons in proxmox, but when I run the auto installation I found an error message containing an order to use linux-header 2.6.32.18-pve. but when i run "apt-get install linux-headers-2.6.32-18-pve" i got message "E: Unable to locate package linux-headers-2.6.32-18-pve
E: Couldn't find any package by regex 'linux-headers-2.6.32-18-pve' "
I'll be glad to receive any kind of help and advise on this matter