I don't think it's worth buying a new motherboard, because you'd need to buy a new processor, new RAM, and I think you may have to re-activate Windows too.
If you really want a new motherboard then say so, it would be good but might end up co$ting quite a bit with the new components.
Personally, I think you'd be better off just getting more RAM and an AGP graphics card and keeping your present motherboard, but that's just my opinion.