+1 for invalidError...
Depends upon how strong your power supply is. Most psus with only a single PCI-E connector don't provide enough amps on the +12V rails to support a high end card. Most are 450W or lower models anyway, so another plug wouldn't help. Most 550W and higher psus have 2 or more power connectors.
If you have a really good power supply with a single PCI-E connector, then a molex converter should work. Note that most adapters convert two free molexes to a single PCI-E plug.
To connect the molex:http://www.xpcgear.com/6pinpciexpress.html
U can find it on New egg:http://www.newegg.com/Product/Product.aspx?Item=N82E16812201004