Since I rebuilt my work desktop, I’ve had trouble getting the ATI drivers to install and behave. Due to the lack of time, I hadn't been able to investigate.
And today, while installing an update (which will hopefully stop the annoying artefacts when running dual screen), it hit me. I was missing a Visual C++ update.
So, if you are seeing InstallManagerApp crashing when installing ATI drivers, go get the update: http://code.msdn.microsoft.com/KB961894/Release/ProjectReleases.aspx?ReleaseId=2067. I’m annoyed AMD / ATI don’t bundle this into their installers to be honest.