Hello,
I've a server with CPanel and CentOS installed and I would like MRTG to monitor the whole server's bandwidth usage, is there any easy guide for how to do that?

Best Regards
Oskar R

The process to install MRTG is basically the same for any *nix based OS

http://oss.oetiker.ch/mrtg/doc/mrtg-unix-guide.en.html