If you are posing the people for the shots the capture software will be fine.

You can trip the shutter with the software.

You cannot compose the shot through the laptop. You still have to look through the camera to see the shot before it is taken.

Speed wise it is a little slower then writing to the card but not bad. If you are posing the students it won't be bad.

The cable that came with your camera to connect it to your computer is the one you need for this. If you don't have it you can get it at any local camera shop, electronics store (Besy Buy, Circuit City, etc..) or also online from places like B&H. However those cables tend to be a little on the short side so you may want to have a USB extension cable just to be safe. You can get those from any of the places above or even WalMart.