Boot Camp Windows 7 on El Capitan MacBook Pro mid 2009

Hi all,

I am attempting to partition and install Windows 7 onto my mid 2009 Macbook Pro running El Capitan.

I have an ISO of Windows 7, have mounted it both using a USB flash drive and from the desktop, however I continually receive this error:

How do I fix this error and how do I install Windows 7 on my Mac? Would it be advisable to do it without the use of Boot Camp (as described here? http://daksh.me/how-to-install-windows-on-your-mac-without-bootcamp/ )

Thanks, Josh.