direct3d help

hi, i want to make a 3d world ,but i did not make choice for retained mode or IM. i know that iM is faster than rm but it gets me harder ... I want to make a simple adventure game,so i only need a room and that has some furnutires into ,also somethings like may be 3 or 4 lights for lightining and also two or three characters..Like this small world,i must use im or retained mode is enough for it.Because in action games like quake III, it is more complex,levels ares so big and has lots of lights,and it has action ,so the speed is everything for it. So what you advice to me,i do not learn rm and pass it or i start from im or is rm enough for adventure game? thanks for all your replies...