I think that most of your trouble is with the graphics card. Integrated video cards are horrible at any sort of high-end graphics application such as Maya. Your first priority should be upgrading your video card. That will make a huge difference in the performance that you are seeing.

XP Home is ok for running Maya. It's not officially supported, but I know many people who are using Maya under XP Home just fine. More RAM is always good. You can never have enough RAM.