I got a Dell Studio Slim and I'm looking to upgrade my graphics card from the Radeon HD 3450 to the Radeon HD 3850. What I want to know is can I still use the 3850 with the existing power supply which I know is 250w, or do I need to get a 450w, and if so which power supply do I need to get that will fit in the case. This is the first time I've upgraded a computer so I'm a bit clueless.