I think 3GB of RAM is simply too little for a complicated scene.  In my experience, a render can fail without Poser telling you it is out of memory.  The crash trying to go back to Preveiw sounds like you were already out of memory and Poser couldn't get the message through.  Texture requirements can easily eat up that much RAM.

I dont know what your upgrade options are, but RAM's pretty cheap.  I'd save the file and double the RAM if you can.  It may be your best option for saving all that work you've put in.

John