Current specs are Athlon 64 3000+, 512mb RAM, and GeForce 5900XT. Game can be quite slow even on low settings, and I fancy a bit more punch. I'm not looking to the best of best, but what can I do that will make the biggest difference to my gaming experience? Can I just buy a new gaming card, or do I have to upgrade other stuff as well?

If you haven't guessed already my tech knowledge is as low-end as my machine......

Thanks.