I haven't had this problem with a similar setup, but using a clone TV tuner card with the BT878 chipset. It works fine no problems.
From memory I'm sure that the Hauppauge card has it's own xawtv setting for the BT878 chipset. As I seem to have noticed that even though it uses this chipset, Hauppauge may configure it in a different way which may be causing the system to freeze.
Other than that there's nothing else that I can suggest...
PS, this was using the old 2960 drivers from Nvidia though..