Are you using W2K because if you are I think that is the reason as I remember reading something about TV cards not working on W2K (or something like that) ... I found it here it is (part of the W2K readme.doc)
TAPI
This section describes issues related to TAPI in Windows 2000.
ATI-TV Tuner Video Cards Are Not Supported for Use With TAPI
TAPI does not support the use of ATI video cards that incorporate TV tuners, including but not limited to ATI-TV, ATI-TV WONDER, and All-in-Wonder models. This will be addressed in a future release.