Cut two plywood boards 18 inches square, and four more 32 by 18 inches. Stand one of the longer boards in front of the overhead projector and mark the location of the projecting lens on it. Cut a hole in the board to correspond to it. If your projector makes noise when it runs, cover the hole with a pane of glass to reduce sound pollution. Cut a notch in the bottom edge of another long panel for the projector's power cable and drill holes in one of the square boards for ventilation.
Assemble the six boards into a cube to make a housing for the projector. The board with a hole in it should be at the front, and the notched board at the back. The ventilated board will make the base of the projector housing, and the other square board will be the top. Screw the sides, top, bottom and front of the cube together, driving a row of screws through each pair of boards along the edges. Attach the back with hinges along one side, rather than screws, so that it can open. Paint the cube black and line the inside with sheets of felt, glued into place. The felt sheets will cover the openings in the box, so cut holes in the felt corresponding to those in the wood.
Wait for the paint to dry and then place the projector inside the housing. Set the projector with the lens facing its opening. Lay an LCD projector panel on top of the projector's glass, and plug its S-Video cable into your DVD player or computer. Plug in the power cords on both projector and panel, and test the system with a movie of your choice. Your media player will display the film on the LCD panel and the light of the projector will shine through it, projecting the footage onto the wall. You may have to adjust the position of the LCD panel to ensure that the image is right-side up and centered properly.
Screw the projection screen to your desired wall, following the installation instructions that came with it. Most such screens are fairly heavy, so have someone help you lift it and hold it in place during installation.
Plug in your speaker system and arrange the speakers as desired. Position the projection unit to center the image on the screen. Focus the projector and connect your media player, LCD panel and speakers.