Have you configured the video capturing?
while the tv is running, right click on the tv window. Select Options -> Configure TV. On the panel that opens, then click on Configure Capture. You can then choose a compressor.
On one of my system I have the ATI AIW Radeon 7500, and the recording works properly.. (although playing back the video, seems to get the aspect ratio wrong.. Huum I probably have to set somewhere a mantain apect ration checkbox that I haven't seen yet
)
Anyway, if you have done this already, then open the Device Manager in Windows (how to do this depends on which os you are using). On Win2k in the devices tree there is a "Sound, Video and Game Controller entry". Expand that node. Look for Video Codecs. Selct the Video Codecs entry and then right click and select Proprieties. In the panel that opens, under the proprieties tab, you will see which codecs you have installed. If you have none, then re-install you ATI sw or look for codecs packages on the Internet
Claudio