MDT: choose specific partition to install Windows on
Solution 1:
You can select what partition/disk you apply Windows to by going to the task sequence and selecting your install operating system task.
After you select it you will notice that there is a section (under the "Operating system to install:" selection box) that allows you to define where the OS will be installed to.
My installation automatically collects the drive letter from the disk format stage and apples to the primary disk automatically (to whatever drive letter the primary disk is mounted to).
Hope this helps!