1 - Boot off the Windows DVD or USB installation media

2 - Choose the "Repair" option, and the command prompt afterwards (the way to get there is different between Windows 7 and 8)

3 - Type in diskpart to get into the partition tool

4 - Use the commands list disk and list part to determine which disk is what. For me, Disk 0 was the HDD and Disk 1 was the SSD. The following instructions assume this

5 - Select the HDD: sel disk 0

6 - Delete all partitions on it: clean

7 - Create a 100MB partition for Windows 7 (change to 350MB for Windows 8): create part primary size=100 (or size=350)

8 - Format it: format fs=ntfs quick

9 - Assign it a letter: assign letter=f (if F: is in use, pick another one. Use list vol to see all volumes and their letters)

10 - Create a partition that fills the rest of the disk: create part primary

11 - Format it and assign it letter "C", as above

12 - Reboot back into the Windows installation media and install Windows into the large partition that was just created

13 - Again, reboot into the Windows installation media and go into the repair command prompt

14 - Use diskpart's list vol and assign commands to ensure that both the boot partition (F:) and the Windows partition (C:) still have drive letters

15 - Select the boot partition (sel part 1) and mark it as active: active

16 - Exit diskpart and type in: bcdboot c:\windows /s f:

17 - Reboot and you should be good to go!

http://superuser.com/a/505059