Boywander - that's a gratifying result. I wonder if your DVD Combo drive is the offender, or its drivers, or a Windows setting? Let us know if you discover more.
ASG - network hardware seems to keep popping up as a major headache in some music PCs, with wireless network adaptor being the worst offenders.
cc. - personally I ran my tests while running my sequencer through a typical song. The measurements when idle on my PC weren't really any different, but being in a real-world scenario seemed the most appropriate method just in case anything kicked in.
mark - I use Process Explorer myself. DPC Latency is more likely to highlight hardware device issues, while Process Explorer may also help you track down rogue software tasks, but can be more difficult to use.
Keep those measurements coming!