I had to find this for someone today, so I thought I'd post it here so it doesn't get lost:

dotnetfx.exe /q /c:"install.exe /q"

What is happening here is the wrapper exe (dotnetfx.exe) is being called with two parameters. The first parameter tells it to run silently. The second tells it to run a specific command after extracting the contents. We then pass the silent flag to the "inner" installer.

Make sense? It doesn't matter, because it works. ;-)