I have experienced the following symptoms with Hyperthreading/Dual Core enabled in BIOS:

-The sound card disappears from Device Manager

- No sound card listed under the Audio tab of Control Panel - Sounds and Audio Devices

- Reinstalling the audio drivers resolves the symptoms until the system is rebooted

 

Upon disabling Hyperthreading/Dual Core in BIOS setup, the sound card problems disappear.

 

We have 10 - Dimension 4600 systems, 5 or more which have displayed these symptoms.

We have 2 - Latitude D620 systems,  and are purchasing 80 more, 1 of which has displayed this problem.

We are running Windows XP SP2 with the latest updates, and all systems are using the onboard audio.