I'm installing Windows 7 on a late 2009 iMac. I've been working on this for a few days now. Due to a hardware issue, I was unable to use the regular Bootcamp support and ended up having to look for a workaround until I found this post.
Exactly which Windows 7 ISO is required for Boot Camp v6.1.0 on macOS High Sierra? MBP mid 2010
I followed all of David's steps and got to this after creating a manual partition using Disk Utility. Then I put in the Windows disk and support and reset the Mac hold option and it didn't show Bootcamp/windows startup. There are only macOS and recovery options.
I tried booting from disk, but the Bootcamp partition still doesn't show up. It said that a problem occurred during the partitioning process, but I don't know exactly what it is. I don't know where to go from here.
A few notes: This iMac is a late 27-inch model with a built-in disk drive, so Bootcamp support only works with physical Windows disks and not ISOs on flash drives.
But since 2009, disk drives have improved so much… I got an external disk drive and burned Windows 7 Ultimate SP1 to a disk. After that I tried running Bootcamp Assistant again, but the disk wasn't recognized at all.
So I decided to follow the instructions in the post. Now I have a partition, but I don't know how to fix it.