One thing I'd recommend is upgrading your RAM
512mb for gaming isn't a lot
To find out the maximum you can have, visit
Crucial.com and click on "Scan My System"
IMPORTANT: The crucial scanner will not work in Firefox, so open it in Internet Explorer if you're not already using it
Or you can post your motherboard make & model (Ex. mine is Gigabyte GA-K8NS Pro) here and I'll dig out that info for you