the 7750 is definate step up from the 4650, but it is still today's low end. the real benefit is it takes all it's power from the slot, no extra power connector needed . the 7770 needs an extra power connector that you either don't have or couldn't use reliably with your current PSU.
is misread your cpu as the older athlon x2, so you'd be fine cpu wise, but you need more power . think to the future and look for a quality PSU min 500 watt
so all i need is changing the psu to 500watt then... my cpu wont bottleneck high end vga then?
i dont want to waste my money to upgrade my cpu, so what is the best vga card to buy by you mean 500watt psu can handle and wont bottleneck my cpu