Oh please every new OS is based off of the previous kernal. Common fact that the next OS will be based off the "current" most stable kernal. Vista is based off of the 2003 SP1 kernal and reworked. 2000 is based of that evil buggy NT4.0 kernal and XP is based of the 2K kernal.
NT4.0 = **** bad evil buggy
Win2K = Ok by my standards good to others
Point is don't judge something by what it's based off of.