Defining Sub-components of items

 Hi,
How do i define subcomponent of an item, let me put with an example.

Eg: Main Item is Computer Item No 800
              Sub component as Mouse 801
                                     Keyboard 802
                                  Power Cord 803
 
So when an order is placed for Computer Item 800, all its sub components should be picked automatically for that order and inventory should be reduce.

How can we achive this? Kindly Help

Rgds,
Amit