only the fastest radiocity render engine that may be able to overcome your memory problem

www.asgvis.com - V-Ray for Rhino 4.0

what are you currently using? have you asked at the NG's? Items in rhino

maybe use a PC with a core-duo and 2 gigs of ram and also turn down the mesh inside your NURBS to a lower setting and work with less complex objects (document properties>mesh >jagged and faster)

sounds like you also need a better graphics card to handle the display in workspace of all those vectors. delete group and hide the ones you don't need after you use them