ISO means International Organization for Standardization. It is a way of making sure that all exposure speeds of film, and digital sensitivity are the same. A low ISO number means more light is needed to expose the film (sensor) to get an image. The low number is also the sharper picture. More light can be
given by either slower shutter speed or larger aperture opening. The slower shutter can cause blur in the photo at low light.
A higher number is better for low light and sports shooting, however it does give more grain (noise) to the image. Most digital cameras can go as low as 100 and as high as 1600. Some advanced digital and D-SLR cameras can go to 3200. 1200 ISO is a fairly high speed and would work well in low light, such as evening outside shots.

Most MiniDV camcorders have a Firewire (IEEE 1394) output connection that will connect to mini Firewire input on your laptop(if you have that connection port). You then use editing software to capture the footage.
If you do not have that connection you can get a DV bridge, such as the Pinnacle Dazzle, that connects to your USB port and allows you plug your camcorder in through the A/V (Audio Video) lines.

Sorry to say they are not. Canon SD630 uses the NB 4L battery, the Canon SD890 IS uses the NB 5L. The NB 4L works on models up to the SD700 IS when the NB 5L takes over.
The shape is different also. The NB 5L is a rectangular battery with three contacts points on one end and the NB 4L is square shaped battery with three contacts on top.

Yes. Power comes from a KLIC-7001 lithium-ion rechargeable battery pack, and an AC adapter for in-camera charging is included in the bundle.