You want something like this:
NCIX.com - Buy nGear 2RCA to 3.5MM Stereo Audio Cable 2M/M 1.5M 5FT - QC-304 In Canada..
You can most likely find another one cheaper.. but whatever.
Just plug one end into your TV's output and the other into your soundcard's line level input.(line_in)
This is assuming that I am understanding what you want.. And to be fair I am not sure if I am.