Vista - ati tv wonder

Sony notebook VGN-AR550E with ATI tv wonder digital cable tuner trying to get
windows vista home premium & media center to receive all channels I
subscribe to from Comcast Cable. Had trouble getting to work at all but
after uninstalling Norton internet security 2007 started receiving all of the
analog channels but very few digital & high def channels. Comcast says
everything looks good on their end & external ati unit has 2 green lights.
High def TV in other room receiving everything fine. I have already loaded
the ati firmware upgrade & any msoft updates that apply to my system. Any
help appreciated....Von