I also have the XPS420 (intel chipset) and had the same error. I got the driver
package and it took a couple of installs and reboots for it to stick. As a convenience, you can download that package here: http://uswave.net/windows7/intel-smbus-drivers.zip
Just extract the files into the folder of your choice, then goto the device manager and update the driver. You have to tell it to manually locate the driver, just put in the drive/folder name where you unzipped the file. Like I mentioned, it took a couple of installs/reboots for the driver to "stick" to the smbus.
I hope this helps (tip my scales