How do I link cell contents across worksheets?

I work for an IT company who build their own PC's. And we use a simple Excel 2003 spreadsheet to piece-together and price-up PC's for retail, I've attached an example of the spreadsheet for you to see. It uses basic formulas so we can see at-a-glance things like VAT figures, margin, profit etc. Each PC we sell is contained within one Excel file, and each PC has it's own Workbook tab.

The problem I want to solve is whenever we change a component or price, we have to do each system manually, which gets very repetetive and time consuming.

What I'd like to be able to do is change the price of, let's say, the motherboard, and have the price be reflected across each of the PC's using that same motherboard on each seperate tab. This same system would apply when we change a product name, product ID etc.

How would I achieve this?

(SEE ATTACHED FILE)

A good way is to use a separate lookup list and the VLOOKUP function to pull back the current values. See the attachment for an example.