Usually graphics cards come with a dual Molex to PCI 6/8pin adapter, so you can wire it up that way.
Should be something like this.http://www.newegg.com/Product/Product.aspx?Item=N82E16812887001
Though I would advise to get a different PSU anyway. That unit isnt 80+ certified, doesnt have Active PFC, efficiency is unknown and although Antec are a good brand, their lower end stuff isnt to be trusted. Also 450W is cutting it fine.
I would recommend this unit. All XFX units are made by Seasonic, regarded as the best manufacturer. 80+ Bronze rating and has features like Active PFC. Comes with a 6pin and a 6/8pin PCI-E connector built into the unit.
XFX Core 550W, 80+ Bronze non-modular. $65http://www.newegg.com/Product/Product.aspx?Item=N82E16817207013&Tpk=XFX%20550W