Like Kees said, it does depend on the software. Some software doesn't use the video card at all, but other software such as Adobe Premiere Pro CS5.5 and I believe Adobe After Effects CS6 rely VERY heavily on any video card that has "CUDA Cores" (Most Nvidia cards). When I got a Nvidia card with CUDA cores it allowed me to go from barely being able to play one 1080p video in real time to being able to play 10 in real time while having effects like rotating video, moving positions, etc (not very processor intense effects, but still). Not to mention that was with a low end CUDA card.
Long story short, check your video software to see if it can use video cards. Then make sure you get a card that is supported by that software.