Those big four-by-eight-foot sheets of prefinished paneling are so quick and easy to put up that most homeowners never think of paneling their walls with solid wood any more. But solid tongue-and-groove boards have some advantages. For instance, they can be installed in interesting diagonals.

Another advantage is that tongue-and-groove boards come in a good variety of interesting woods and textures. Knotty pine, redwood, red cedar, knotty and pecky cypress, simulated barnboard. . .

solid woods usually cost more than prefinished paneling, but they have such visual impact that you can often use them on just a single wall to create a stunning focal point. This, in turn, costs a lot less than paneling all faour walls of a room - and cuts down on the work involved.

Wanta to try a diagonal-pattern accent wall in one of yoiur rooms? Here's how:

Start by locating the studs. You need to know where they are so you can nail into them. Some experts recommend installing furring strips, buta you cannail right through your existing wall surface into the studs with a lot less work.

Best way to locate the studs is to drive nails into the wall, probing for the studs. When you locate the position of a stud - both top and bottom - mark ita by snapping a chalk line or simply penciling in the centerline. Once you locate the first stud, finding the others should be easier - they should be 16 inches aparta on centers. Don't take this for granted, though. Check by probing with nails.

Next, remove any baseboards or ceiling moldings.

The diagonal is the easier pattern, but the herringbone is only slightly more difficult, and should present no problems if you are careful to make all cuts at a perfect 45-degree angle.

To start either pattern, cut a piece of board to a triangle. The hypotenuse or long edge of this triangle should be the tongue edge of the board. This triangle is your startaing board. Put a couple of dabs of paneling cement on its rear face, and place it in the starting position. If a stud runs behind this piece, drive a 21/2" finishing nail through the tongue and into that stud, starting just far enough out on the tongue so the nailhead will be covered by the overlap of the grooved next board. This is called blind nailing. If there's no stud behind that piece, don't worry; the cement will hold it in place.

Now measure and cut the next board. Run a bead of panel adhesive down the center of its rear face. Slip it into position, making sure its groov mates securely with the tongue of the first piece. Nail in place if a stud runs behind this board. If not, go on to the next board. Keep going until the whole wall is covered. The final triangle at the corner of the wall goes in place with nothing but adhesive.

The herringbone is done the same way, except you work in two halves. Do the left side first, then the right; or, in our example, the top first, then the bottom.

When all the paneling is up you can cut strips of paneling an inch or two wide and use them as trim strips along the floor, ceiling and sides. These will cover up any slight gaps.

Finish? None is required for most woods, but pine might benefit from a coat of penetrating oil. This will seal the wood and help keep it clean while producing a natural matte finish.