Can I transfer Windows between PC's

Hi guys, I am a about to build a computer and stupidly did not budget for windows.  Now, I could use linux for free, but what i was wondering is: if i have a laptop already running windows, can I transfer some files and in essence transfer windows between PC's?

No not really. I wish you could though. 

Edit: You can copy things like documents/ pictures/ steam folder ect.. but not the operating system itself.