Basically you need to do this:
Have two physical hard disks in your laptop, and laptop's BIOS should support booting from either of some (some laptops cannot boot from the secondary hard disk).
Install Windows as usual.
Convert both hard disks to "dynamic disks" (in the Disk Management, right-click on the hard disk to access menu)
Right click on the system partition, select "add mirror", and choose the second hard disk as a target.
You could do these steps when partitioning during the install, but it's not really needed... It's easier to do after the install. You'll have to wait the initial mirror sync, though (computer is usable but disks will be busy).
Notice: I personally found Windows soft-RAID very picky... Any bluescreen or unclean shutdown will throw the mirrors out of sync, resulting in lengthy re-syncing afterwards. Go with hardware raid or fakeraid if possible at all.