Apple Mac OS X Users - I suggest that you think of Cacti as more of an appliance and installing it on OS X Server will not only be a bit more complex but the constant upgrading of updates may break your install after you spend a lot of time going through the trouble to get things running properly. Instead I suggest that you build a VMware/Parallels image so that it is more transportable in the future. We have found traveling from tradeshow to tradeshow that this works great, back ups are easier as well. I also suggest that you look at creating this in Ubuntu as this is the next easiest server OS and everything is detailed to getting this up and running with tons of plugins.
If you want to build the cacti monitoring server from scratch then read below. Please note that this is a fresh Ubuntu 8.10 VMware image with nothing installed except for SSH server.
Update and Upgrade - I went ahead and ran the latest patches for the OS.
Install AMP - (Apache MySQL PHP)
apt-get update apt-get upgrade
Now we need to install Cacti and it's components
apt-get install mysql-server apache2 apt-get install php5 php5-gd php5-mysql
After you configure the information from the Cacti installer then you will need to change some of the information in Cacti after changing the password.
apt-get install cacti-cactid
settings > paths > Spine Poller File Path [ /usr/sbin/spine ]
settings > poller > Poller Type [spine]