Gear inch/ratio question

Gear ratio: number of teeth on chainring, divided by number of teeth on rear sprocket, multiplied by wheel diameter (in inches) gives you a gear ratio. This is the theoretical diameter of the wheel with that gearing. To make it easier to understand multiply that ratio by 3.14 (or to be strictly accurate pi) and that will give you the distance you will travel for each revolution of the chainwheel.

There are a number of sites that might help you undestand gearing. Try Highpath Engineering: http://www.highpath.co.uk/
In the left-hand side menu click on c'Cycle information' then 'Choosing your gears'

Or try Sheldon Brown: http://www.sheldonbrown.com/

Thanks for the links and info... I think I'm beginning to get it all now.
...and to everyone else who gently prodded me in the right direction - cheers !