correct, produce alot of assasins, and try and lv them up if u can, i produced 3-4 assasins in cordoba(sp) in my moors camp, and then, after i got one to lv up, i got offered the guild. also they are quite a good unit, in my experience they stood up to most european heavy inf, and dismounted knights, and if u can get the guild early u can have a very big advantage over ur enemies specially when u get the "best unit u can train" reward for council quests.

Cheers Knoddy