De acordo com:
https://help.ubuntu.com/13.04/serverguide/preparing-to-install.html
estes são os requisitos mínimos de hardware para o 13.04:
Install Type CPU RAM Hard Drive Space
Base System All Tasks Installed
Server (Standard) 1 GHz 512 MB 1 GB 1.75 GB
Server (Minimal) 300 MHz 128 MB 700 MB 1.4 GB