You may register in advance by filling in the registration form on this site, or you may register during GAP.7 in the conference office.
As a member of GAP you will only have to pay a reduced conference fee. (The exact price categories you find below.) Of course you can join the society before registering; either go to the conference office or visit the webpage of the society at www.gap-im-netz.de.
To take advantage of the early registration fee, you must have registered by 1 July 2009.