you might be able to recover the data by putting a second drive in as the master and installing XP to it. then add the original drive as the slave and pulling the data off of it.
Can you get to the boot menu at all? (where it allows you to choose safe mode, etc.). If you can then try the Enable Boot Logging feature. This will create a log file and help you point to what is causing the error. You would have to hook it up as a secondary drive on another machine to get to the boot log file.
There is also a Disable Automatic Restart on System Failure option you can try. That will stop the reboot and just hang when it locks up. Then possibly you can see where it is locking up at.
let us know if that works.