Ralph, Drill the hole at one end of the prospective slot, get a rat tail file just a bit smaller than the hole and grind away.
You might try drilling and pushing sideways on the board, but you'll end up breaking bits. You can get router bits pretty small but when they're that small, assuming big enough for a number 4 screw or the like, the surface speed of the bit gets pretty low and they're not efficient. A file's the way to go unless you've got lots of holes. Tom Fowle
