Cut a piece of 56-by-14-by-1 1/4-inch piece of plywood. Sand the cut edges using medium-grit sandpaper.
Cut a 14-by-1 1/4-inch groove in the side of a 32 1/2-by-2-by-2-inch post using a router. Make the groove 1-inch deep. Center the groove on the side of the post 2 inches below the top edge of the post. The top edge is the end of the post you want up.
Repeat Step 3 a second time on a second 32 1/2-by-2-by-2-inch post. Make the groove the same size and depth as the groove on the first post.
Paint or stain the two posts and the plywood sheet the desired color. Use two coats if necessary. Let the pieces dry overnight.
Fill the two routered grooves with wood glue. Insert the plywood sheet into the grooves in the two posts and push the posts together to secure the plywood. Wipe away any wood glue that squeezes out of the grooves.
Hold the headboard upward. Place a standard metal bed frame against the headboard. Position the posts against the metal bed frame connectors. Use a pen to mark the screw holes in the metal bed frame on the wood bedposts. If necessary, have someone help you with this step.
Drill a 1/2-inch hole through the bedpost where you marked the holes in the prior step. Hold the headboard back up to the bed frame, aligning the drilled holes with the holes in the bed frame. Insert a 4-inch bolt through each of the holes. Place a washer and nut on the end of the bolts and tighten the nut with a wrench.
Set your mattress and box spring up on the bed frame.