Before you can create a 100Mb partition you have to reduce the size of the 'C' Drive. This will create Unallocated Space which can the be used to create your new partition. Windows doesn't like changing C, so download and run EaseUs Partition Masterhttp://download.cnet.com/EaseUS-Partition-Master-Home-Edition/3000-2248_4-10863346.html
Go to the Main Screen and select C.
Simply move the slider from right to left until you have reduced C by at least 100Mb
Create your new partition in the Unallocated space you now have and apply. As C can't be altered with Windows running, the changes will be completed on restart.