The Holochamber was the Rec room aboard the Star Destroyers. Combat programs run by the computer allowed Lord Vader to practice various stages of realistic, intensive battle simulations.
The chamber was made using segmented trays from boxes of bon-bons (trays used to separate each individual chocolate candy) fashioned to appear like the walls within a holodeck facility. The floor was assembled using an overturned plastic food tray with one of those holographic pictures glued in the center (the electrical currents appear to move when viewed from different angles) - just happened to find this one at a local book store. The base measures 12" wide by 12" tall, total 4 sides.
Vader was put together using several different pieces, with the Unleashed Vader as base. Because the Unleashed series didn't have any articulation to begin with, Hasbro Vader parts were used to allow movement. Got the cape from a ML Magneto, and whittled a plastic red stir-stick into his lightsaber.