The system for entry is simple. Any enemy fought within your level range will drop a token, which can produce one of two items. The first is an NVidia box which includes useful in-game items and certainly is nothing to sneeze at. The second is a raffle ticket, which automatically puts you in the drawing for one of the graphics cards, with more tickets meaning a better chance of winning a card. Aika players are also given a special page to track their entries, something that will no doubt become quite frequent as the event marches on.
[Update: We've changed up the graphic with the most current one per the folks at gPotato. Note, the event runs through the 13th, not the 18th!]