Okay, I booted into Windows 7 now. To re-enable it, go to Control Panel -> Sound -> Playback Tab. Then right click on the white area of that screen, and check "Show Disabled Devices". After you enable it, then you can just mute it through the microphone properties.
Side note: Don't make the mistake of enabling "Mic Boost"! I did this and I almost went insane with all the clicking, popping and screeching. I would move my hand across the palmrest and there was a terrible, god-awful screech. Every key-press resulted in a sharp pop. The worst part was, I didn't realize I had enabled it!

Hunter Thompson
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inkPad T400: T9400, 8GB, LG WXGA+, Samsung 830 128GB + WD Scorpio Black 500GB, Intel 5300agn, Win7 Pro x64
Others: IBM ThinkPad R40, Sony VAIO NR Series, HP TouchPad running CM9, Jailbroken iPod Touch 4G