Find an old hardcover book that will not be missed. You can usually find old books that are being discarded at your local library or school. I found this old hardcover book at a thrift store for about $2.00.
Make sure the book you chose is slightly larger than your netbook in all dimensions (width, depth and height). My netbook measures 260mm(w)x184mm(d)x30mm(h) [10.25"x7.25"x1.25"], the pictures show how much room I had left around the netbook when comparing it to the hardcover book. You want a snug fit, so try and find a book that closely matches your netbook.