The power supply is a concern, but pretty sure I have seen other models of HP computers with a similar power supply and they come with something like this,
Newegg.com - Computer Hardware, Video Cards & Video Devices, Desktop Graphics / Video Cards, Radeon HD 6000 series, Radeon HD 6450
Very low power requirements (about 18W for the card at load, and even less for general use), comes with both the DVI port you want and a HDMI port. Not a world better performance wise by any stretch of the imagination, but still better that the onboard Intel you have now.