I assume you know how to boot from USB/CD etc and have all the installation software you need?
First, install Windows. Don't worry too much about drivers/service packs etc. Once you get the first welcome screen, Shut down.
Secondly install BT5.3 - During install you will get the option to Install backtrack/ubuntu alongside windows 7. Make sure you select this. Install Backtrack up until main login.
When you restart your computer you will be given the options of Windows and two ubuntu options - You will need to remember what one is what, or look into GRUB2 menu editing so you can rename the options at login.
Thirdly, install Ubuntu. The same option during install will appear for installation of Ubuntu / Windows - It will either create it's own partition or install within backtrack partition - I can't remember exactly.
I personally would install Just Windows and Ubuntu, and keep BT on a USB stick - Runs very well that way and can be set to remember who you are and save your settings as you use it.
There can be lots of issues that may crop up but if you let me know here I will do my best to answer them. Make sure the computer you are installing to has nothing important on it. Things can and do go wrong during these processes.