Perhaps you misunderstand the meaning of the Dump files... It may not be the USBStor.sys is the cause, or that BSOD said USBEHCI.Sys is the cause...
Sometimes all the Dump file is reporting is that those devices dumped what they had in storage... but usually the DMP file is not reporting a cause... only that something caused the DMP or Dump from those devices.
In our experience, the HP Windows XP Media Center Edition or its communication with something in the m7730 is the cause. In our three county area, no relatively new machine gives us as many service calls as an HP machine with WXP Media Center Edition... and we have seen that a lot of them were sent back to HP for a rebuild. Some were replaced. Some had major hardware replacements.
So if still under warranty, or the problem is something that started with your HP when it was still under warranty, we suggest you call HP Tech support with your notepad full of notes about the history of the problem... or send them a long and detailed report that you have spent some time writing so that it can be helpful in getting things corrected.