Hi Jim,
First of all, I just want to state I'm by no means professional in this, but have ran niteclubs / events and have used similar tactics which worked extremely well.
It can be quite expensive to rent these projectors but over the course of the last 2 years I've bought 5 as I used multiple projectors on some sites / events.
All of these have been moving images, with the brand of the club/event and flashing lights / changing images, static images dont really attract peoples attention.
The wall which you need to project on should be ideally white, but cream / yellow will also work.
What is the distance between the window and the wall?
I live in Meath, if you're close I'd have no problem showing you the setup and software that I used.