Installing Windows 7 and Ubuntu 12.10 on external hard drive

Hey guys.

I don't really know what I'm doing so I'm posting for step by step instructions for installing Windows 7 and Ubuntu 12.10 onto my external hard drive using Mac OS X Mountain Lion.   I have a 2012 MacBook Pro 15" with retina display so I have a Thunderbolt external hard drive which is fast enough to run Windows and Ubuntu on. I have looked online  instuctions, and either the instructions are for Windows users, presenting a problem seeing as I'm trying to install Windows or for Mac but the intsructions aren't very clear. 

Again I want Mac OS X as my main OS everytime I switch my laptop on but when my external drive is plugged in via Thunderbolt I would like to have the option of either Mac, Windows or Ubuntu to boot from. 

Can anyone help me?

I would not recommend you do that, for an OS is too important to a system and a lot can go wrong when using an extrenal device, also it will more than likly be slower thatn if it was connected via sata2 or sata3.

You unconnect all other drives in your system, and set the load order to load from usb first. This will be a permanent change. You need to make that change in your BIOS. Then put in your install dics and it should install onto your device.  

Don't know how you install Windows, exactly but theoretically you just have to choose the external hdd for both, the installation and the boot loader. After that you can install linux and again install the system and the bootloader on the external hdd. Make sure to install windows first because it will fuck your bootloader up otherwise. When you boot you just have to set the correct boot order or select the drive manually. Not sure what Mac uses for booting (bios, uefi?).

if you just add the partitions and install to them, it should work. you will have to manually boot from the external though.