Bike racks are readily available for most cars and SUVs, but there aren't many selections available for pickup trucks. Once you've got the necessary parts, it should only take you an afternoon to make.
Measure the width of your truck bed. If necessary, cut the 1-by-4 inch board to fit your truck bed's width.
Mount the board to the bed of the pickup. Mount the board with the bolts, lock washers and nuts, 18 inches behind the front end of the pickup bed. Drill two holes in the bed of the truck and secure the bolts from below with the lock washers and nuts.
Mount the two universal bike mounts to the board with wood screws. Position them far enough apart that you can mount two bikes in the bed at the same time. The bike mounts are available from performancebike.com (see Resources, below).