Build a wall. Putting up a freestanding, prefabricated wall is an ideal temporary room-dividing solution. You put together this portable, interior partition yourself and place it wherever you need it. Find them online or in a home-furnishing store. Temporary walls are durable and sturdy, constructed from such materials as wood, acrylic, glass or aluminum. They come in a range of not only colors but also styles, so you can easily find a design that will complement the decor of your room.
Make a wall with furniture. Try a folding screen, which you can purchase or make yourself by attaching three lattice screens, wooden panels, doors or something similar together with hinges from a hardware store. Another option is to divide the areas by putting a large piece of furniture between them: a wardrobe, china cabinet, bookcase, entertainment center or comparable piece is big enough to act as a wall and also has the necessary visual weight.
Make a non-traditional wall. This is a good option if you want some but not total separation. Create a half wall between the two spaces: use a row of large potted plants or artificial trees or a couple of benches. Line up a row of tall vases, and put spray-painted tall branches or decorative sticks in them. Install a ceiling-mount track for hanging curtain between the spaces — opaque or sheer depending on how much separation you want.