In some cases, binary packages are provided by the apcupsd team (Red Hat, Mandriva, Su SE, Windows, Mac OS X).For other platforms it is recommended to check your vendor's package repository and third party repositories for recent binary packages.
MODBUS (see below) is required in order to access the advanced data.
This is the keyword to specify if you are using your UPS in Slave mode (i.e.
the machine is not directly connected to the UPS, but to another machine which is), and it is connected to the Master via an ethernet connection.
apcupsd is a complex piece of software, but most of its complexities are meant for dealing with older hardware and operating systems.
On current hardware and software getting it running should not be very complicated.