Just here to give a big thank you to Dosdude and others who have made getting Sierra on my MBP Mid 2009 with no problems at all a breeze.
Just a couple of things that happened that others might like to know.
I have a 500gb SSD, 8GB Ram and a 750gb HDD (the SSD is in the Optical Drive Bay and currently has El Capitan installed on it. Most data is on HDD (all user folders are linked to where they reside on HDD).
I partitioned the SSD to give me one volume with El Capitan and one for Sierra. That way I could install Sierra on the partition and not lose anything on El Capitan if it didn't go to plan.
I used a USB flash drive first to make my installer but at only 8GB and probably pathetic write/read speeds I could not boot from it.
So attached a WD external HDD, partitioned it to make one half available for time machine and the other for the Sierra installer.
Ran the install as documented in the guide, when system went to reboot I got prohibited screen. (White screen and a no entry icon in middle).
So turned off MBP rebooted back to El Capitan, then rebooted again to Installer Tool, and ran patch tools (and installed legacy USB support which I guess was what brought up the prohibited screen up).
Booted again and chose the New Sierra install which started up. And allowed me to start setting up options.
Went back to El Capitan ran TM back up to WD Ext HDD, and now I am currently waiting for Migration Assistant to complete, hoping it keeps all user folder links, and Photos library remains linked to correct place. I am all backed up to iCloud so should all be good, hopefully it doesn't start running a whole re sync.