For some reason this will not work for me these are my server settings
#Minecraft server properties
#Mon Jan 31 21:03:39 CST 2011
could it make any difference that I am using this on a mac?
That should turn monster spawns off. Make sure you stop the server, check server.properties and make sure it's still the same, then start. Sometimes weird things can happen if you're editing while the server is running.