If i use parallels do i need a windows 7 key?

Yes, you need a Windows 7 DVD or disk image (.iso) and a valid key.

 

plus your windows version need to be allowed for virtual installation. For Vista it was the ultimate (and I think Pro or business); for Win8 I have the Pro version running under Fusion. Win7 I'm not sure.
But you will need a key and you might even need to call MS for activation (I needed for Win8 as I "burned" my first try).

 

I think with Windows 7 you can install without the key and it will run for a certain amount of time unactivated, it isn't really a trial though.

 

The Trial version is for 180 days and yes it needs a key as well.

Without they key it will run for 30 days.

 

Parallels simply allows you to install your own copy of Windows on an OS machine. Parallels does not include Windows.