How do I take TV audio and plugit into my PC
 

I have been using mediaportal and well ,it has been working pretty good but I just want to use part of media portal ( accessing video files) and use my TV for TV . but I want my audio coming from my TV which has rca output jacks and plug them into my PC so I can use the head phones from my PC for sound while watching tv, I can do this right now but I down liike the dellays when changing channels in media portal but I like the sound quality of my Xonar dx card so how do I do this. do I get an adapter that converts the rca audio out to the Xonar card ( haven't looked at it quite yet) ? and when I am watching tv will I be able to hear the output of my TV or would I have to change something in the audio config?

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.

thats what I thought Thanks