looking at his config i dont think the psu will have enough juice to run 550t or a 6770 as i seriously doubt a stock psu to have a 6pin connector rail
if we get the psu wattage and the wattage on the 6pin rail if any we can suggest something. as far as 6100 is concerned, as the other guy said its onboard integrated and u should look for a more dedicated gpu. Your processor will do fine but dont expect it to play games great even if u upgrade ur psu and graphic card to a much better one, as im sure the 64x2 4200 will bottleneck higher end cards.
please provide psu wattage and mobo info