Sorry, if I mis-read your question. OK, to go from an HD timeline to SD videotape (which format are you trying to layoff to - BetaSP?) you will need an I/O interface.
One of the more poplular I/O's are the AJA units. They have I/O's for every budget and format, HD in/out or less expensive Analog I/O etc which connects either to your computers Firewire port or is a dedicated PCI Express card. These have either HD connections and/or Component video, analog audio and RS422 ports for machine control. You can use that to layoff to SD tape.
http://www.aja.com/products/io/io-hd.php
There are other companies that make these interface I/O's, but many of us swear by AJA products and their unparalleled customer service. I have both the IoLA and Kona 3
