What is VIDEO DAC SNOOP in the BIOS setup?

This is a Dell Dimension 8250 with a P4-3.06 HT processor, a gig of ram, and a GeForce FX5900XT(128mb) video card. I recently came across an article that mentioned hyperthreading being enabled or disabled, and that if you are running programs that don't take advantage of hyperthreading, having it enabled in the BIOS actually degrades performance.
I looked into my setup-as Dell calls it, and see that Hyperthreading is enabled. While there, I noticed this "Video DAC snoop" setting. Mine is disabled(I bought this computer second-hand on ebay). It came with an ATI Radeon 9700pro card. I got rid of it(problems in Far Cry and Doom3), and installed a GeForce FX5900XT.
Can anyone tell me if this Video DAC Snoop should be enabled or disabled?
Also, do you agree that enabling HT in the BIOS is the wrong thing to do? I have yet to come across a program that works with, or uses HT.
Thanks.

 

Thanks Pete, you're a gem.

My computer generally performs well. I really have no complaints with the hardware. I recently started getting some grief from a program called RegSeeker. Otherwise, all is well.
Thanks again.

 

Thanks TonyT

This all really started when I downloaded an update to Quake 4 that, among other things, improved the performance in the game by taking advantage of dual core, and, I thought, HT processors. I downloaded and installed the update, but Quake 4 locked up, no matter what setting I tried. I uninstalled completely, and reinstalled the game itself. It runs fine. I might re-read the instructions in the update to see if I misunderstood something.
Thanks again.