#1- Put in an operating system disk. (Would probably do XP first).
#2- Boot from disk and enter Windows Setup. (XP setup is easier to format partitions).
#3- When you get to the partition managment screen, make sure you have a fully blank HD with no partitions. Create 2 partitions of the size you want. Remember to multiply the number of GB you want to use in the partition by 1024 in order to get the correct # of MB to set.

#4- On drive C:, begin install of XP.
#5- When XP install finishes and works correctly, pop in the W7 disk. Restart.
#6- Boot from 7 disk and enter Windows 7 Setup. When it asks you to either Upgrade or do a Custom install, choose Custom. Select your D: and install W7 to that drive.
#7- Windows 7 will most likely reboot during the install so when it does, your BIOS may prompt you which OS to boot from. Select Windows 7.
#8. After all is installed, you can reboot and pick what OS you want to boot.
Hope that was English!