There are no "Dell restrictions" on what you install on your PC.  In fact Dell has both Windows 7 and Windows 10 drivers available.  [URL]
Few days ago i bought a dell inspiron 3567 laptop and it comes with Ubuntu OS. But by today i want to install windows OS to my laptop . so , i thought to install windows 10 and windows 7 as a dual boot for my laptop . But before installation, My friend said that  " it can't install windows 7 to dell laptop . Because dell company had a agreement with the Microsoft company and then they not allow permission to install windows 7 in my laptop , but i have chance to  install windows 10 in my laptop ". So, i want to know that can i install windows 7 in my laptop and make a dual boot with the windows 10. Please reply soon as you can .... 
How to install windows 7 and 10 as dual boot for inspiron 3567 laptop