What kind of drivers are you looking to write? When I worked for ATI, customers were looking for info on their GPU's so the could write drivers for it. In order for them to do that, they had to purchase a developement package from ATI that provides all that info. I'm gonna guess it's going to be the same for anything else you want to write drivers for.
Check out this Canadian website(well, it grew too big, so now it is actually international):
They have some articles about drivers development, although they seem to refer to MS DDK which is $200($199 to be precise). But anyway, you can contact people there, maybe you can also find some one who is willing to work with you - post on the msg board.