I also have an Pinnacle PCTV card.
First you should know the following:
Look at this
pic
From the top the plugs are: TV-IN, Audio-Out, Video-In(RCA), Video-In(S-Video)
The PCTV card slots into a PCI slot through which it transfers the decoded Video stream. The audio has to go from the Audio-Out on the card to your Line-In via a supplied cable. Some models also have an internal Audio-Out that connects to you Soundcard's CD-In or Aux-In plug using a simmilar cable to the one you use to connect your CD-Drive's Audio-Out. (Usually a thin grey cable)
There are two ways to watch tv.
1. Via Normal TV cable (Coaxial - solid core, stranded shield)
Run a normal tv cable from your TV aerial or MultiChoise decoder's TV-Out to the TV-In on the card. In the TV-viewing software you select Tuner for video input, tune to channel and select apropriate Audio input.(External - Line-In / Internal - CD/AUX-In)

- Easy to setup, Sharp Image, One cable from Decoder to PC

- Mono sound
2. Via RCA Cables (Red, White and Yellow plugs)
Video and Audio run on seperate cables.
For Video: For this you will need a simple RCA to RCA cable.
Example.
Run the RCA->RCA cable from the Video-Out(Yellow) on the Decoder to the Video-In((Yellow) on the PCTV Card.
For Audio: For this you will need a Dual-RCA to Headphone-jack cable.
Example.
Plug the Red and White RCA plugs into your decoders Left and Right Audio-Out plugs (Red->Red, White->White). Plug the Headphone-jack into your soundcard's Line-In (blue) plug. In the TV-viewing software you select RCA for video input and select Line-In for audio input

- Stereo Sound, TV-out on decoder is free to go to TV

- Image isn't as sharp, Lots of Cables
Hope this clears up some confusion caused by the *cough* smoke *cough* above.