Needing help with Bootcamp Drivers on my late 2009 27" iMac running windows 7 64-bit.

Hey, installed Windows 7 on my late 2009 27" iMac (Have previously done so and worked flawlessly, magic mouse could scroll etc) but had to remove the partition as I required more of my hard drive than anticipated, so I removed the partition and went to install Windows, everything worked fine until I wanted to install the bootcamp drivers, to which it said that my Mac doesnt support 64-bit... which it does as I've been running it for months with no problems whatsoever. Would appreciate if someone could tell me which version of bootcamp would be best to install and how to do so if the procedure isn't that simple. Also I get no sound from the Windows partition, as I get a red light from the audio Jack, which is clearly from the lack of drivers as it works fine on the OS X partition.

I have snow leopard install discs handy although the version of bootcamp on that differed from the one I had, which was much better.