LR4 film grain versus LR3 film grain

I believe they are the same sliders but the effect might be different with the new engine. In any case I would advise you to upgrade to LR4.1. I was in the same boat as you. Had Windows XP and LR3.6. It was a good excuse to get a new computer and am still amazed at how fast LR runs compared to my old machine. LR4.1 is very powerful and you get much improved results over LR3.6. I also very much like Windows 7.