Did you allow the Windows install to create the 100MB partition by default? It's part of the MBR or master boot record.
Basically, that's it. What I've done in the past is to create a 64GB partition to install Windows 7 to, and leave the other partition as a "miscellaneous" one, for downloads and storage.
Actually I make the partition a 65639MB size, which is 64.1GB, then the Windows install makes the 100MB partition and leaves the partition then as a 64GB size. I install to it. Like I said the remaining part of the hard drive I make as another partition for the other stuff.