er... I think you mean 1tb hdds surely ,A 1GB hdd is not big enough .64bit windows 7 typically takes up 17-18gb initialy ,and will quickly grow well over 20gb once you start installing 3rd party apps .
In answer to your question ,yes you can install as many copies as you like onto the same machine ,this does not breach any microsoft rules as the rules state you can only install on a single machine at any one time . and that you must not run more than one copy at a time .
neither of these rules apply ,for no matter how many installations you put on your single machine you can only be using one at any one time .so no agreement will have been breached.and there will be no fear of your software becoming blacklisted (the key) as your hardware will be identical for each machine and as a consequence windows update will assume you have only one OS.
I use a product called HyperOS ,it will run several copies of any OS (within reason) on the same pc .and will allow you to copy /clone .OSs to other drives and manage and create backups too .