Sometimes you want tight control of the partition that Windows is installed into. For instance, with Windows 7 you may want to avoid the 100 MB system-reserved partition by presenting the installation with an existing partition. I don’t care much about the 100 MB but I do care about losing one of my four primary partitions when building a dual/triple boot system. It turns out the answer is very easy, using diskpart:
Hack to remove 100 MB system partition
Using diskpart


Some useful notes on which bits of C:\WINDOWS can be deleted: