Pinnacle PCTV and Jitter

Hi all,
it looks like I can't get my PCTV USB 2.0 tv grabbing card to work
properly with Jitter. I am using the jit.dx.grab object, and even if
it's recognized in the device list, I don't get any entry in the input
list. When I try to open the device, I get the error messages:
-could not render capture stream
-could not build preview graph

Where is the problem in your opinion? The card has multiple inputs
i.e. composite, s-video and TV channels. How can i get full control of
it in the max environmentt? cheers
Alessandro