depends on your uses but i will opine.......... the hard drive is slow ( 5400rpm )....... unless you use the 320 for main drive...... dual cores are kind of useless but will still work. i don't buy low end graphics cards but if that's the final piece the 550 is better than what you have now.
Your best upgrades are to go to either an FM1 board, Asrock makes a great board for $75 on newegg with the Llano 2.9GHz chip w/ 6550 integrated graphics. With this, get an 8GB (2x4Gb) set of DDR3 1333 Ram. Total will run you around $260.
Or, go with a Phenom Zosma 960T as it is a true quad core with the potential to unlock a 5th or even 6th core, and is easily OC'able. This should be paired with an HD6950. Your board will support it. Total will run you around $280