as apokalipse said, it would be good if you have an AGP slot,
you could get a decent video card to whack in there for around $230 AU or $130 US depending on where you live.
Onboard video is quite often a problem with games these days, as it uses your memory up... so theoretically, you could increase your RAM, and it would make somewhat difference... However, if you have the extra $$$, you would be much better off purchasing a new video card.
If you have no AGP slot, then RAM is your only avenue, otherwise, you will need to buy a new motherboard that has at least AGP, but more importantly, you should aim for PCI - e in today's market.