Its just the load on the processor, as long as its got decent cooling then I shouldent see a problem, I've left my desktop rendering for about a week running at 100% once with no probs, and I pretty much just use it as a rendering PC now as I've got my laptop.

As for your laptop you could get it to render using both cores (so it will be faster) but I cant remember how to change the settings!

Was the Quadro 4 750XGL (PC) quote your graphics card? If so the graphics card dosent do anything with rendering (unless your hardware rendering of course) its only the processor, RAM etc if your using the Maya Software and Mental Ray rendering engines.