Hello,  Well, Don Teach and Nicholas Simons got pretty close to
the right answer (he said bravely).  In fact, what they said will
do the job quite well.  If you want to get fussy about it, though --

First, get a set of plug cutters starting at about 1/4" diameter
(then perhaps 3/8" and 1/2") so you can make the smallest plug that
will be larger than the hole.  Then find some wood that is the same
as the part you want to repair: old wood that has a similar grain
structure, _not_ some new, half-dried stuff from the home center with
three annular rings per inch.  You want something that matches the
original and is slightly dryer, if possible.

Now, make a few plugs with the grain going across the plug _and_
at the same angle as the original wood.  If it is quarter sawn make
the plug quarter sawn.  If the grain is parallel with the surface, make
the plug the same way.  Then drill a small hole in the center of the
plug -- smaller than the screw hole will be.  This is easier if you do
it before you pop it out of the board you cut it from.

Drill a hole in the original board  to match the plug size, just to
the original depth of the screw hole.  Now, coat both the inside of
the hole and the outside of the plug with yellow wood glue.  (Remember,
this doesn't need to be taken apart later, so use the best glue you can
for the purpose.)  Now, line up the grain and tap the plug into the
hole.  It's okay if it sticks up a little.  Trim it with a flush
cutting saw with no set (and/or a chisel).

You can use a normal maple dowel as a punch to tap it in.  If you
drill a small hole through this dowel, the glue that squirts up through
the little hole in the plug will just fill up the hole in the dowel.
Cute huh?  This way, the plug will go all the way to the bottom of the
hole without being stopped by the hydraulic pressure of the extra glue
in the bottom of the hole.  You might even want to put a slight bevel
on the end of the plug to match the bevel on the end of the drill you
used to make the hole.  The glue will swell the dry plug slightly and
make it even tighter.

Lastly, use a tapered drill to match the screw and drill to the correct
depth down through the tiny hole you made as a glue vent.  The end will
be tapered to match the core diameter of the screw.

If you'd like to add some strength to the screw hole, try this after
the glue is dry:

Screw in the screw to the desired depth.  Back it out part way and do
it a couple more times to 'form' the threads.  Then remove the screw
and drip 3 or 4 drops of "super glue" into the hole.  After putting
a thin film of wax or light oil on the screw, turn it back into the
hole, being careful to turn it into the new threads.  The "super glue"
will harden the wood fibers in the area around the new wood threads and
make them much stronger.  When the super glue has set, back out the
screw and reassemble the parts.

Regards
Craig Smith