Fortunately the answer is rather simple: If you have the capability to use a DVI Cable, feel free to take advantage of it! All that is required is a Flat Panel Monitor (CRT monitors cannot take advantage of DVI like Flat Panels can) and Graphics Adapter that have the white DVI port available. Simply connect the cable at both ends and ensure the Flat Panel is setup to receive a Digital Signal.
On the other hand, the VGA cable can carry RGBHV video signals: Red, Green, Blue, Horizontal Sync, and Vertical Sync. The VGA socket is made up of 15 pins in three rows of five pins, and typically colored blue. The cable socket is securely attached to the device using two screws, one on each side of the socket.
Although DVI provides a higher quality signal, the differences between DVI and VGA are not readily apparent to most computer owners. However if you look closely you will likely notice the more vibrant colors and crisper images available using a high quality Flat Panel and Graphics Adapter.