Hello,
First, you may have noticed the website uses both e17 and SMF.
SMF doesn't sound so opensource (
http://www.simplemachines.org/about/opensource.php ), while you can get it for free.
e107 is GPL.
So you can get the PHP scripts.
The design was made by Udi, it reuses OpenArena GPL textures and it's likely the CSS is GPL or at least shareable, though I don't know if there are any repository where you can download it, you could eventually rip them, or bug
Udimanche or Fromagedel'enfer to get some zip with it.