Several fixes have been suggested. Try these and let me know if any work for you.

Disable Enhancements
* Go to Control Panel- Sound
* Right click on the Speaker/Headphones icon and choose properties
* Click on the enhancements tab
* Select the Disable all enhancements check box
* When finished, restart the PC

Disable Wireless A band
* Go to Control Panel- Device Manager
* Click on Networks Adapters
* Double click on the wireless card
* Go to the Advanced tab
* Select from the list Disable Bands
* Select the A band from the list on the right side and disable it
* When finished, restart the PC

Disable Quickset LightFX
* Double-click the Dell QuickSet icon in the Notification Area
* Click the LED Effects tab
* In the XPS LightFX Music Player Plug-ins area, click to unmark the checkbox next to each music player
* Click Apply. The installed plug-ins will be removed

Choppy audio was due to Secondary IDE CD device being set to PIO
Run PIOtoDMA.exe to set the Secondary IDE CD device to UDMA mode

Remove the Dell Sigmatel driver and use the Microsoft High Definition Audio Device 6.0.6000.16386 driver (installed with Vista itself)
Of course, you lose the ability to install the Sound Blaster Audigy ADVANCED HD Audio XP software