It will depend on the construction of the drawer itself.

basically, replace the drawer box w/ a new one, but put it in upside down. Re-attach the decorative front.

In some cases, the decorative front is an integral part of the drawer box, and you'll need to cut it away; in those cases, the new drawer box should be a little bit shorter, back-to-front, than the old drawer box so the front can still be flush w/ the desk.

you might want to try to get a drawer box that doesn't have an inset bottom (basically, four sides, then nail a sheet of masonite across them to make the bottom), though that slight inset would sure keep the keyboard from falling off.

Be sure to ask this over at the Woodworking forum! Post pics of the desk and of the drawer in question, if you can

Here is a link that might be useful: our very own Woodworking forum

You should be able to remove the drawer completely, along with its drawer slides, and replace it with a pull-out keyboard shelf. Most of them are screwed to the underside of the countertop. I think they cost between $35 to $65, from any office supply store, like Staples. Measure the opening to ensure what they offer will fit and that it will be at a comfortable height for typing.

While not fancy, inside the existing drawer we piled a few National Geographics under the keyboard. It raised the keyboard enough for us to be able to use it, and the front of the drawer provides a bit of a wrist rest. Works like a charm.

You can also take off the drawer front and hinge it along the bottom so you can fold it down toward you. the keyboard can be stored in the drawer with other things (if not wireless you can cut a hole in the back) and when closed it looks normal but when pulled out and the front flipped down, is just a keyboard shelf/drawer.

You could use Styrofoam panels from the crafts store to lift up the keyboard, too!

Or these Iris "project cases" to store stuff (I keep my P-touch labeler in one, stationery in another, etc.), and set THEM under the keyboard to lift it up.