I presume that you've followed the instructions for sideloading the iMac Windows drivers into your install via USB stick? (wasn't aware the EFI recognized the SD slot as storage on boot. Now i know)
I always found more success in just slipstreaming the drivers and install.xml file onto a custom Win7 DVD rather than the USB approach when trying with my Late 2009 27" iMac. The Win7 installer needs that enclosed .xml file in the driver package to tell it where to find the drivers so that they be loaded when the Win7 image extracts itself.
If you're using mountain lion, then you should be receiving the proper Win7 driver set. If you wanted to create a custom image, then you can use an ISO file, the driver package and disk utility to make something you can use. Either that or you learn what edits your install.xml file needs to point the installer properly and check it manually.
I don't know what links you have so i'll just include everything:
Installing boot camp on a Late 2009 iMac:
Direct link to Late 2009 iMac-specific Windows drivers.
I'd try a USB stick and the iMac-specific driver set. It should steer your insolent windows installer correctly.
Hope this helps.
Thanks for the reply.
The Drivers directory contains the following ATI drivers:
Are these the correct drivers?
Is there any way of checking if the drivers installed correctly to rule out that this is the actual problem?
Is it actually possible to install the drivers via Parallels, i.e. boot Win7 in Parallels and then install the drivers from disc?
Just so that i'm crystal clear on the problem that you're actually having, you're making it through the Boot Camp procedure successfully right up to the point at which the Win7 install configs have completed, it's rebooted and you're presented with a black screen when the Windows Desktop loads. DId I get this right?
The ATI drivers included in the download pack from the link I included are good, albeit out of date. The trick is to make sure the Windows installer is loading them as the windows install is occurring. It's easy to tell as you're either going to get a black screen when Windows loads or you'll see the Windows Desktop. It's either success or fail. Once you're actually on the windows desktop, then the video drivers can be updated to current relatively easily.
Trying to install the drivers using Paralells won't work because Paralells isn't loading the native windows drivers/devices to run windows that the ATI drivers need to be associated with. Rather, everything needed to run Windows under Paralells is being run on virtualized hardware that Paralells is providing, rather than your iMac itself. The end result is that the drivers would get applied to the virtual hardware coming from paralells, not to the physical video card itself.
Keep me posted.
I've also encounter this same issue after getting my 27 iMac HDD replaced. None of the other driver downloads and what nots work. BUT..... here's what I ended up doing and worked perfectly.
1. Attached an external display while system in still in Mac OS and ensure that second display is showing my Mac OS desktop.
2. Reboot into Win7 OS (iMac display should remain blank).
3. You should see the final steps for Win7 OS installation on the external monitor.
4. Complete Win7 OS installation.
5. Launch Control Panels and go into Device Manager
6. Locate Display driver and update using the driver you've downloaded from http://support.apple.com/kb/DL995
7. As soon as the display driver is updated, your beautiful iMac display should now be mirroring what you see on your external display.
8. Install Bootcamp that came with the iMac (labled iMac Mac OS X Install DVD)
Hope this helps.....