Heres a step by step guide to getting a free Windows key.
Step 1. Get in your car (or walk or take a bus) to your local McDonalds. (Or a similiar fast food restuarant in your part of the world)
Step 2: Fill out application.
Step 3: Get job.
Step 4: Save your rupees.
Step 5: Buy Windows 7. Comes with a free key.
Stop being a cheap bastard and buy it. No one here will give you a key, or tell you any other way around validating Windows 7.
On another note, if you don't want to pay for an OS (operating system), there are free ones. Try Linux. I read an article saying that Linux Mint is a good one, totally free and easy(er) for those new to linux. Or, if you have a school software program, you might be able to get a free (legitimate) copy of windows OS software. Ask your IT department.