I need help selecting a graphics card for my HP Pavilion?

My HP Pavilion 8000y Media Center PC is just under 6 years old. I need to replace the 512mb ATI Radeon X1700SE, 2 DVI graphics card with something equal and compatible. HP no longer carries the part. The original card is 6 and 5/8ths long.
The computer's O.S. is Vista 32bit; with an Intel Pentium III 2.4GHZ duo core processor.
The hard drive is 500GB, while the RAM is 4GB DDR-2. The power supply has a maximum rating of 350 watts.
I'm not a gamer, however, I edit videos, and work a great deal in photo-shop. Also perform a good deal of audio work.
Hope you can guide me to finding a suitable replacement.