Are ATi video cards supported?

Yes, but there are some limitations.

The open source Radeon drivers are enabled out of the box, and will work with almost every ATi graphics card on the market. The open source Radeon drivers are great for 2D acceleration and video (even HD video will play fine), but may be insufficient for 3D gaming use. For more information, consult this web page: https://help.ubuntu.com/community/RadeonDriver

The official ATi binary drivers, which have full 3D support, have incomplete video support due to their heritage as workstation drivers. If you use the official ATi binary drivers, you will likely have issues with video playback. For more information, consult this post: http://phoronix.com/forums/showthread.php?t=23020

If you have an ATi graphics card, I recommend that you stick with the open source drivers but be fully aware of their limitations. The open source Radeon drivers are the only drivers I will be providing official support for in infinityOS as they are the only ATi drivers that fully support playback of HD video.

Note: In future versions of infinityOS, the open source Radeon drivers will have full 3D support.