Felix,
I have a HP Photosmart 3210xi connected to a router via Ethernet and use ImgBurn with no problems... Though I am running on Windows XP Pro SP2 and not Vista (I won't even consider Vista as an option until at least SP1, and perhaps SP2 with all I have been hearing from my peers). Have you tried to disable any of the unnecessary things the HP is doing at startup to see if that resolves the issue?
Best of luck,
SithTracy