27in iMac (late 2009) ATI 4850 drivers problem in Windows 7

malku wrote:
Hi
I have installed several times Windows 7 on my imac 27 with ATI Radeon HD 4050. I want to try what you did, downloaded the catalyst 10.4, but still don't know how to install manually 8.723.0.0 is't the one that comes with Catalyst 10.4 or do I have to roll back to another driver version like explained in other discussions?.
Please help me, I need to get working with Autocad 2010.

I've been waiting for the answer, Would you pls post it here? Thank you! Anybody can answer it?

I was looking for this answer myself.
After having now searched for hours I finally found the answer on another forum and I thought I would share it in here.

Basically the solution is a new driver, but to be allowed to install a new driver we need to modify the .inf file first.

This worked with my iMac 27" - Ati HD 4850:
VERY step-by-step... sorry

- Download the desired driver ( I use the driver from this post 8.723).
- Start the very first install, it will unpack into the selected folder.
- Then after it having unpacked, cancel the installation.

- Locate the folder with the .Inf files ( eg. C:\ATI\Support\10-4 vista64_win7_64_ddPackagesDriversDisplayW76AINF )
- Open any of the 2 .inf files (doesn't matter which) in notepad.
- Replace the lines which contains the name "ATI Radeon HD 4850"
So that it equals = ati2mtag_R7X, PCI\VEN 1002&DEV_944A&SUBSYS00B5106B
Like so
*"ATI Radeon HD 4850" = ati2mtag_R7X, PCI\VEN 1002&DEV_944A&SUBSYS00B5106B*
- Save the file.

- Open device manager, selected the Ati-card, press update driver...
Select "Locate and install driver software manually"
Select "Let me pick from a list..."
Select "Have disk..." and navigate to the folder with the modified .inf file.
Choose "ATI Mobility Radeon HD 4850 Version whatever "
It will warn you that the driver is unsafe - ignore this.
If you are as lucky as I, your driver should now be installing...

Hope this might help someone

Just to confirm, when I install the ATI Catalyst package, it will only install and update the drivers and it does NOT install ATI Catalyst application. I remember for my PC I use to get an ATI icon at the bottom of the desktop that I could open up to check out the drivers, video card setting, etc. However, it seems that in Bootcamp, it does not allow it to install.

Is that correct? or is is that the ATI Catalyst no longer installs this application, and is for the drivers only.

This same thing is happening with my MBP 17" Core Duo (Non-Unibody). All of these instructions/problems/drivers seem to be affecting people with iMacs... Anyone have this issue with a machine like mine? Obviously the drivers would be completely different...

Seconded....I have the color banding problem in bootcamp/win 7 64 bit. I would really appreciate a more detailed walk-through. Sounds like the mobility drivers are the way to go?