I would say you are fairly optimal considering the old video card. I wouldn't advise lowering the settings anymore, otherwise you will lost most of the game itself. You are limited most by your memory on that machine. I would advise to upgrade the memory to 2GB and replace the videocard. If you get cheap 2nd-hand memory and videocard the processor will do ok. I am guessing you might be using onboard video, in which case the memory is certainly the limiting factor, as you are probably sharing between videocard and system memory.
I have run PR -passably- on some very very low spec machines, as low as an 1.5GB - AMD duron 1800 with some overclocking
, on AGPx4 Geforce 7200. Thats about the bare minimum.
A new videocard will work wonders if your machine can take it. Just ask Mongol how much better it was afteri advised him to buy a new one.
