Hi neo99!!
This is actually one of the most common issue. I think I know the results after you get the new drive, there is a high possibility you might be still be unable play HD-DVD.
I did research on this case, and this is the thing I found related to your issue. If you still unable to play the HD-DVD after replace the drive, you can do this. (Make sure you return the original drive to HP first before continue to troubleshoot, or else you might be charged

)
Install this updates:
HP Patch 1
Install this updates:
HP Patch 2
Install this :
Update your laptop chipset/BIOS
Warning: Check your current BIOS version before update this. Or post back if you not sure about this step
Finally, if it still not working, you might read this article:
Vista issue
Hope this helps you