In the past, support for specific GPUs was built into the client. We are working on ways to automatically update this information more easily within the v7 client to support new GPUs, such as the Kepler GPUs which have just came out. While the automatic update isn't ready yet, here is how one can manually do this:
1) Download the GPUs.txt file from https://foldingathome.org/file-releases/public/GPUs.txt
2) Copy the downloaded GPUs.txt file to the client's run directory. The run directory is also called the data directory. In Windows there is a link to this directory in the start menu.
3) After installing the file you must restart your client.
The client has a built-in GPUs.txt which it will use if it does not find one on disk. The client will print a message to the log, very early on, when it reads GPUs.txt from the run directory.
In a future version of the v7 client, this will happen automatically, but for now, we are updating this file on our web site and donors can do this update manually for new hardware.