All PowerMacs come standard with an Ethernet Port built in. The ports on the Macs are actually "gigabit" ports, which are 10/100/1000 Base-T ports, altough he'll probably never get on a gigabit network, it's still a cool feature. So yes, an Ethernet port is built right in to connect to a network, cable/DSL modem, etc.
And his current PC monitor will certainly work. The PowerMacs come with a DVI-out and an ADC-out (specific for Apple Displays) and it also comes with an included DVI-to-VGA adapter, so even if his monitor is VGA, a cable is included with it to allow him to connect right into it. Hope this helps!
