I tested that theory by simply disabling the sound driver in Windows 7 to see if that stops the sudden shut down, but it didn't on my Latitude D830 laptop computer.
On my D830 computer I've narrowed the problem down to the Windows 7 NVIDIA graphics card driver. I've replaced the heat sink assembly and installed a new fan becuase I thought it was an overheating problem but it didn't stop the sudden shut downs.
I ran Windows XP and even reinstalled Windows 7 on the computer. XP ran fine. Windows 7 ran fine until the first set of Microsoft updates that were automatically downloaded that included the NVIDIA graphic card driver were installed. Shortly after restarting the computer with the new NVIDIA video driver active, the sudden shut downs started again.
So I need to try to manually install Dell's Windows Vista NVIDIA drivers in Windows 7 and, if that fails, Try Windows 7 32bit otherwise it's back to Windows Vista.