vtcop,
Keep in mind that even if there are USB peripherals out there that can transfer S-Video over USB, you're going to be limited in bandwidth if you're using USB 1.1. At only 12mbps, you can only transfer 1.5MB per second max. My digital camera takes like 30 seconds to transfer 12 pictures at that speed. For video, I couldn't imagine how long it would take. So, I doubt using your USB connection will be worth it.
Just my 2¢
~cdogg
"The secret to creativity is knowing how to hide your sources."
- A. Einstein