Thanks for that - the demo is almost perfect as it is - even the right colour!
I have adapted it slightly and using your example discovered the GraphicsPath class which should be more efficient. The problem is it's difficult getting it to create single pixel diagonal lines especially on non-45 degree co-ords which is what I need. WIP.

I have yet to re-create the Windows.h problem although I have discovered this in another of your examples (BringMeUp.) The syntax seems pretty obscure to me!
Code:
#pragma comment(lib, "user32.lib"
I will come back on this when I have time - thanks again.