Back to your original question, your choice is either to buy a new tuner for your PC (PCI card or USB device), or use an external tuner built in to, for example, a VCR, and capture the VCR's composite output with the PDI Delux card.
I can't say for certain which would give the better quality, but I'd be tempted to get something for your PC - it would cut out the need for a length of composite video cable from the tuner to the capture card.