Step 3 - Installing Windows Vista
The hardest part for including Vista on the multi-boot is already done, you did that in the previous step.
All you need to do now is find your copy of Windows Vista and boot from that DVD at boot and begin the Vista install process, as normal.
The only real difference is that when it comes to choosing where to install Vista, you need to make sure you pick the new partition you setup and labeled for Windows Vista - if you labeled the drive during formatting in Windows 7, it should be very easy to pick out.
DO NOT pick the wrong partition as it will break your Windows 7 install.
Once Vista has been fully installed, reboot and you'll have the option of booting either Windows 7 or Windows Vista from the boot menu. That was easy, huh?
Now we move onto Windows XP, which is more complicated, but easy enough if you follow the steps.