Hooking my TV sound into my computer

It depends on what sort of audio output options your components have.

In my case I have a dvd, d-vhs, and ps2 that all have optical outputs, and a TV/set top box that will only output sound via an RCA jack.
I run all of the optical devices into a 5 port switch which runs to the computer, and on to the speakers. For TV I run the RCA cables into the breakout box that my creative soundcard has. ( NOTE they do sell RCA -> 3.5mm headphone jack adapters, but I don't know if they support surround sound that way )
The optical devices sound great but, in my case, TV doesn't sound too good mostly due to the limitations on control of source audio. Also sometimes an feedback loop can occur when people, other than me of course, start turning on devices without paying careful attention to mix levels first.

so my craptacular diagram looks like this

dvd player --+switch+-computer-Speakers
dvhs player -I..........I
ps2-----------I..........I
tv/stb-----------------I

Jam it back in, in the dark.