How can I customise a keyboard layout?

[djn1]

Does anyone know how I can customise a keyboard layout? I'm using the Dvorak layout and want to change the mapping of shift-3 ... it currently gives me the "#" when I would prefer the "£" symbol (i.e. it's a US layout and I would prefer a UK version). On the face of it this sounds like a fairly trivial request but having spent around 10 hours searching the net I've now got quite irritated by the whole business and would be really grateful of any assistance.

Thanks.