Just lookin’ at the specs you provided, you probably would make out better by getting a good video card. The integrated card is hogging CPU resources, and the one on that board (according to what was listed, only 256 Mg. isn’t so good). I think you would find a great improvement over all. You would probably need a new power supply, if you are less than 500 watts.
I think a new processor would not make that much difference, based on the board specs, and if you change the processor, you will have to pay for your OS (VISTA) again, as a processor change makes Micro$oft consider it a new machine. You might be able to con your way out of it. Call late at night, when you get an Indian (from India) tech. They are usually really cool about these kind of things. Just tell them that it is the same computer you have had all along. It has worked for me, when a MoBo failed and I could not get the same one again. The Video card (get one with 1G memory) is where I would start, cheaper way to go, you won’t have to worry about your Vista certification. Start saving for a new computer after that. I really prefer ATI.