umm... Udai, you shouldn't update your card yet, as Jag said, you need to change your PSU in for at least one with 450-500 watts. Any of the 5xxx series recommends a 400 watt but go higher, you never know. Also, your mobo is a bit outdated :P i must say that even updating the card. You will see performance hold backs. As your mobo only has a 16x/1x PCI express slot. Although 5670 is backwards compatible with the old 1.0 16x slots. You'd still see a drawback. So be sure to get the 16x diamond 5670, or this one. http://www.newegg.com/Product/Product.aspx?Item=N82E16814103104
The reason being this card especially runs on Pci express 16x 1.0 oh btw i don't think there are anymore options for you other than the 1gb card for pci 16x express 1.0.
Sorry for any errors. Hope it helps. It is a bit on the expensive side though just saying.