Why do you need 256MB memory for photo editing? You do know that the video card has nothing to do with photo editing right? You can use the simplest of cards as long as it meets your dual monitor needs with Dual RAMDACS and dual vga/DVI outputs.
A 16/32 MB Matrox card would be more than enough. You would only need that much memory on a vid card if you ran CAD apps or play games. And another thing, there arent too many video cards that are powerful enough to utilize that much RAM in the first place.
X800 series for ATI or better can use 256
6800 series for Nvidia can use 256.
The card you mentioned "ATI 9250 256MB DDR AGP" is a marketing gimmick. Although at that cheap price, it doesn't matter.
For the BEST 2D experience I would suggest Matrox for your needs. They have always been the 2D champ. Maybe a G550 would serve you well.