Before getting too far along it would be prudent to tell us your Service Tag number of your Dell and we can check to see if Dell has Windows 7 drivers for that unit - or you can check yourself.
If they don't have Windows 7 drivers some folks have good luck using the Vista drivers on a Windows 7 install - sometimes.
Have you decided the Windows Edition (Home, Pro, etc.) and architecture (32 or 64-bit) of your desire? Of course you cna't put a 64-bit OS on only a 32-bit capable system.
I'm glad you already know how/where to download a Windows 7 ISO already, right? It won't be from Microsoft.
I'm glad you already know how to take the ISO you download and how to make a bootable DVD or USB device, right?
When you hunt on Amazon for that 25 character Product Key it must match your Windows Edition for it to activate properly. I guess links are not necessary, right?
I'm pretty sure you will not be able to purchase a HDD with Windows 7 already installed and expect it to work in your Dell.
Edited by joseibarra, 18 June 2018 - 08:41 AM.