OK, so here is my experience with and solution to these problems.
I was also unable to download Windows Support via Boot Camp Assistant, just like everyone here.
I decided to go ahead and use the Snow Leopard disc instead and said that I had already downloaded the support files.
After installing Win7 Ultimate x64, I inserted the Snow Leopard disc and attempted to run the Boot Camp setup program. I received an error that said "Boot Camp x64 is unsupported on this computer model". Turns out that although many MacIntels will run 64-bit Windows, Apple only lists a few as being supported. There is a workaround for this to install the drivers so your keyboard, trackpad, iSight etc. will work properly.
Open the disc in Windows Explorer and navigate to Boot Camp>Drivers>Apple
Right-click on "BootCamp64.msi and select "Troubleshoot Compatibility".
(note: I used a USB mouse to do this since the trackpad drivers weren't installed to allow right-clicking)
Another window will open up in a moment. Select "Start the program".
For some reason this allowed all the drivers to install and everything is working as it should.
Please note that only certain computers will receive the "Boot Camp x64 is unsupported on this computer model" message. If you do not, then continue to run the Boot Camp installer and run Apple Software Update to receive the latest version of Boot Camp.
I would also suggest installing rEFIt. It's a free EFI-based bootloader that allows you to choose your OS at startup, as opposed to using Startup Disk in the Control Panel/System Preferences or holding down Option upon startup.
It's a free download available at
http://refit.sourceforge.net/
Hope someone finds this helpful!