|If you have the CD that came with the TV tuner card, install the software for Windows 7 for it from the CD.|
If you don't, or if you do but it doesn't have Windows 7 software, go here and get it:
You don't need to install Catalyst again for it. You don't need to install the ATI TV tuner viewing program.
After the software has been installed, you need to set up the TV tuner in Media Center as well