best for your build:PowerColor AX7750 1GBK3-H Radeon HD 7750 1GB $89.99
very attractive price performance:MSI R6670-MD1GD3 Radeon HD 6670 1GB $64.99
$49.99 after $15.00 rebate card
both are substantially better than what you have. however the second card being PCI-E 2.1 may have
a problem with your PCI-E 1 slot . . .