does your onboard video support shadermodel 3? if no then upgrade your system with a seperate video card that does eg any currently available geforce/ati video card(unless notebook then you should give up) OR you could (if fiancially able) buy a new computer to replace your five+ year old system.
win xp does NOT needed admin mode, that is only for vista/win7, and AA refers to the videocard driver Anti-Aliasing settings to blur the edges so that lines at angles look a bit better, but from what little I remember about the intel g31 video, it does not offer AA, so the AA fix could not help you.
harpo