On-board AC'97 5.1 Sound acting up

I've got a computer that's about 2 years old (P4 2.66GHz) running WindowsXP Pro SP2. I've been having issues with it running slowly, flakey audio, etc, and finally just did a format/reinstall (sweeping it with anti-virus, ad-aware, spybot, etc had little effect). Everything runs great now, except the audio. I checked some settings, the cable connections, etc, and discovered that the problem lies in the front left/right channels on my built-in AC'97 audio chipset. If I swap out the plugs for the front and rear audio, the front speakers can play the rear channel's audio, so it seems nothing is being output on the front channels at all. I'm just wondering if anybody else has ever had this problem, and what I can do to fix this; the front channel being out really causes problems, as most media doesn't include 5.1 audio encoding (I first noticed the problem streaming media from the internet, and when trying to use Skype/Gizmo).

So yeah, any advice would be great. Thanks.

 

Go to Control Panel>Sounds and Audio Devices. On the volume tab click the advanced button under speaker settings. Make sure the correct speaker setup is selected.

 

I already checked there, and it is set up for "5.1 surround sound speakers ". I also went into a seperate entry in my control panel, "Sound Effect Manager" (the AC97 audio configuration utility). In that, under the "Speaker Configuration" tab, I have it set for "6-channel mode for 5.1 speaker output ". It was using this configuration program that helped me first find out that the front channel wasn't outputting any audio.