Im thinking about upgrading my graphics card and power supply

You don't need to spend 100.00$ on a PSU for that particular computer... Unless you HAVE to go modular....

Antec earthwatts EA500 500W Continuous Power ATX12V v2.0 SLI Certified CrossFire Ready 80 PLUS Certified Active PFC Power Supply - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371007

and this :

SAPPHIRE 100253HDMI Radeon HD 4650 512MB 128-bit GDDR2 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Low Profile Video Card - Retail
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102829

The antec EA500 is more than enough for anything you install on that PC...And you have a beefier video card.....

 
* OS: Windows XP, Vista, Vista64
* CPU: 3.0 GHz P4, Dual Core 2.0 or AMD64X2 (or higher)
* RAM: 1 GB for XP / 2GB for Vista
* Disc drive: DVD-ROM Drive
* Hard drive: At least 7.5 GB of free space
* Video: Direct X 9 compatible video card -- Video card must be 128 MB or more and should be a DirectX 9-compatible with support for pixel shader 2.0 (ATI 9600 or high. Or, Nvidia 6600 or higher)
* Sound: Direct X9.0c compatible sound card

My guess is yes... as long as you don't use xAA

And make sure you have enough Ram.....