Hi there.
USB on most DV camera is not designed for full quality video transfer. It is more designed for still pictures and video clips, most cameras offer a poor quality clip though, mine does same when i try USB, mostly due to other devices using USB. Also some cameras offer a software mode switch between USB 1.1 and USB2, make sure if you have this that you use USB2. Some DV Cameras (even now) still use the much slower USB1.1 as thier USB interface for transfering basic small clips and photos.
S-Video is low quality and you need a video capture card built in to the machine with S-Video. Most machines which have S-Video are only an output to display the PC screen (poorly) on a TV.
I personally would only use a DV cable AKA Firewire or i-Link to transfer onto the PC. USB is shared bandwidth whereas Firewire is much faster for sustained transfers. The video picture is much easily transferred and higher quality. All you need is video capture software (which it looks like you are using to capture via usb).
On the camera side is the small 4 pin "i-Link" firewire connector.

On the PC you usually have the larger 6 pin connector:

Although laptops commonly could have either 4 pin or 6 pin. Desktops are mostly 6 pin if fitted.
If you do not have firewire then cards to fit into PCs are usually very cheap. for example PC World (where i work) did a firewire PC Line PCI card + cable for £14.99.

For laptops you would need either a PC Card (PCMCIA) or Express Card Firewire adapter. If you have one of these slots it is usually on the side of laptop.
PC Card:

Express Card:

*Note this is a dual Firewire 400 (right) and firewire 800 (left) card, most cameras and cards are 400.
Boring side note. Even though USB2 is up to 480Mbps and Firewire is up to 400Mbps in real world firewire way outperforms USB2 in most cases due to the way USB allocates resources to the attached devices.
I am a geek btw

- I repair computers for a living :>