I normally render at very high resolutions.  Poster size and some custom sizes like 36x42 at 300-600DPI.  It can take a week to get one good render at that size and resolution but it is more than worth it when you take it to kinkos to print on their lino machine.  As stated before watch just where it is crashing.  It is probably a bad misbehaving object or shader.  I notice that this occaisonally happens to me when rendering certain combinations of refraction, reflection and transparency.  It most often happens when I have 2 or more overlapping objects with some combination of those properties in certain proportions.  Check for that.  Also some objects don't seem to interact very well with shape primitives.  Also watch memory and virtual RAM, it fills up incredibly fast.