AGP card for the "last hoorrah" before upgrading.

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Check this out as an option. It is only about $60 more than your budget... but it is a full upgrade. Also, it is a AM2+ mobo, so at some point, you could get a Phenom (I know... not as good as C2Q, but the setup is cheaper).

Mobo
http://www.newegg.com/Product/Product.aspx?Item=N82E16813135074
49.99

GPU
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102700
74.99

Ram
http://www.newegg.com/Product/Product.aspx?Item=N82E16820134635
38.99

CPU
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103774
55.99

I know this isn't the greatest stuff anymore. But, it is a lot better than what you currently have and with the AM2+ socket mobo, it leaves a lot of options open for future upgrades. The only possible bad thing is the board is a mATX, but I am sure you could find a full size board for a similar price.