If your iMac came with a snow leopard disc, all the drivers are on the snow leopard disc. If you have a newer imac with lion, you will have to get the drivers from someone with a similarly new imac.
if you have snow leopard insert disc when running windows and install bootcamp, if this does not work install drivers manually from the folders on your disc.
if you run lion, go to bootcamp and follow script to burn bootcamp assistent and choose option download latest support blabla
it would be a lenghty process but what if you install OS X use bootcamp assistant to make the drivers, than format HD install windows and use the drivers you just made? would this work