Sorry to tell you but I just did a quick look and your video and audio on that motherboard dont have support in Win 7. So to use that computer in Win 7 you will have to get a dedicated graphics and Audio card.
This is your videoVideo Adapter
Intel® Integrated 82865G http://downloadcenter.intel.com/Detail_Desc.aspx?agr=Y&DwnldID=18576&ProdId=1044&lang=eng
I am assuming that the Audio is Intel integrated so most likely no joy for that either. 2 options go back to windows XP or get a dedicated video and Audio Card.
My suggestion wait tl you can get a better system not worth throwing money into that system at all.