Thanks Chazly - and all - great answers!
I think my Maths knowledge is not up to doing those conversions though...
I remember a guy once who programed a scientific calculator to convert 1:25000 grid coordinates on a map (to 8 and 10 figures - very accurate) to lat/long coordinates on the globe (is that WGS 84? I can't remember!)
He was a very clever guy though...my head hurts just thinking about it!
Any help or explanations appreciated - but I realise I might just have to put the lines on by hand and 'mark one eyeball'
Cheers guys
Stew