Sorry, not sure if this has been done to death (difficult to search), but I was wondering if AWADers agree with this style guide on the above - it seems fairly sensible to me:

setup, set-up, set up
There are subtle differences between these three. Setup, a noun, is common in modern computer parlance to mean the installation of a computer program and can be used by extension to refer to the creation of an entity such as a company.
Create a setup file in under 40 days.
Setup costs and monthly fees can be exorbitant.
Set-up with a hyphen (also a noun) should still be used to refer to an organisation or arrangement already in place,
Nice set-up you have here.
or to a fixed contest or ambush,
The knockout in the fourth round was a set-up.
I didn’t realise that it was a set-up; even when I found a horse’s head on my doorstep.
The third option, set up, follows the rule of many adjectives where the addition of a preposition gives it a more precise meaning.
‘Sue Ridge Plumbers’ was set up a few years ago and has regular clients.
Also note that a tennis player may at some point in a match be a set up.
http://www.unisa.edu.au/staff/copystds.asp