You can adjust the priority of a program but there is typically no purpose for single-user computers; what priority does is control what order a given process (or program) is allowed a turn on the processor, as the processor gives a portion of its "attention" to each process that has sent it an interrupt (a "pay attention to me please" signal).  Since pretty much all single-user computers, when you hit your Render button, aren't likely to be doing too much else that requires a lot of CPU time, adjusting priority rarely has any useful effect and can often cause you problems like Angelouscuitry describes.

While it would be nice if you could set a quota on a program to prevent it from consuming more memory than you have, unfortunately this is not a feature of Windows (or MacOS I'm fairly sure).

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