Found an old pc of ours in a closet and thought I'd set it up in a kid's
room. It's a custom built. Has plenty of RAM memory, a CD burner, floppy
drive, DVD drive, and 80gb hard drive.

A problem, leading to a question is: the pc has only a dialup modem. Also,
one empty slot.

To set the pc up to connect to Ethernet (hub/router), is it as simple as
adding an Ethernet NIC card in the extra slot?