The Domino Designer download is actually an "all client" kit that has Notes, Designer, and Administrator in it. You can get an install Administrator (actually all three clients, that's the only way to get it) via this download:
http://www.ibm.com/developerworks/downloads/ls/dominodesigner/?S_CMP=LSDL
But the page you're asking about should also have the similar all client kit available from it, but it appears it is just the Notes-only kits. We're asking what's intended and if the trial page description is wrong.