A 430 is not powerful enough for the effort, if games is your goal.
This 530 has a quad core ? My e4500 530 has a 300 watt psu.
The gts 250 uses probably a little more power, than a gts 450, 55nm vs 40nm.
The next step down is a AMD card, the 5670 , it requires no power connectors and is about 20% less powerful than the slowest gts 450. Its a good compromise, if you don't want to invest in a new psu.
edit: I just bought a 30 dollar bronze rated 500 watt psu, to put in a dell 530 along with a ATI 4770. I use it for my movie/tv show viewing.http://www.newegg.com/Product/Product.aspx?Item=N82E16817152040