Solution
I had this exact same issue. After using Apple's USB flash drive driver package to get Windows 7 to actually install, the display would freeze repeatedly, often with pink artifacts, and then the driver would stop responding, then recover. In case you haven't managed to fix it yet, let me share my solution with you.
1. Disable Aero effects temporarily (will decrease frequency of crashes).
2. Download ATI Mobility Radeon 48xx Series drivers for your version of Windows 7 32/64-bit (MUST be Mobility Radeon), located at:
http://support.amd.com/us/gpudownload/Pages/index.aspx
3. Run the EXE and allow it to download the remaining driver package (will be another EXE). Save the package to an accessible location.
4. Run the EXE you just saved. It will unpack into C:\ATI\Support\. Once it's done unpacking, close the Catalyst installer.
5. Pull up Device Manager (found in Control Panel on Windows 7), expand display adapters and right click Radeon 4800. You want to update the driver.
6. Point the driver search wizard to C:\ATI\Support (include subfolders).
7. Once the driver is installed, the version should be something like 8.712.0.0, and you can restore Aero. Problem solved.
If you want to ensure that this problem does not surface on subsequent installations of Windows 7, you can replace the ATI drivers on your USB flash drive with the ones you just downloaded. Delete the old files and drag the new folder over. Keep the unattended installation script in the root.