Tri-booting windows 7, windows 8, and linux

There are two ways of triple booting Windows 7 + 8 + Ubuntu 11.10
1) Have Windows 8 control the booting
2) Have Ubuntu to control the booting
Windows 7 cannot boot Windows 8.

If you choose 1):
You can install Windows 8 a) to free partition or b) to VHD

If you choose 2) you have to install Windows 8 to partition or Ubuntu will not know about it.

Best would be Method 1) b) - Windows 7 and Ubuntu on partintions, Windows 8 to VHD

To install Windows 8 to VHD - there are plenty of tutorials on the internet. Follow one of them.

At this point you would have all three OS installed but only Windows 7 and Windows 8 present in boot menu.(Windows boot menu - Windows MBR)

The last step is to create an entry for Ubuntu 11.10 in Windows BCD (boot config data) store. You can use this clean and easy solution:

Copy file "/boot/grub/boot.img" from Ubuntu to Windows 7 partition - best in Windows "\" root folder. (This step can precede Windows 8 install as you have a dual boot install to start with - if later you can use the utility "ext2fsd" to access Ubuntu from Windows.)
Now create a "BootSectorLoader" in BCD and give it as "BootSectorFile" the file "\boot.img" - see here -> http://www.boyans.net look for how to create Linux loader.