I did the same thing myself just a few years ago. The best way I found to accomplish this task, is you'll need to prepare and repair the wood on the stairs themselves. As long as your stairs aren't made of plywood, this shouldn't be too difficult. You'll first want to sand the stairs, to remove any residue fromt the carpet, also, to prep them for staining. Use a power palm sander and this process will be much quicker -- also, be SURE to sand with the grain. If you sand AGAINST the grain, you'll see the scratches in the wood. You'll then want to make sure to repair any holes, cracks or other noticeable defects with either a wood putty or wood glue. Make sure to use products that are meant for wood, as other products won't blend in as well. Once the putty or glue has dried, sand that area once again to make certain it's flush with the rest of the surface. Now, once all of that's complete, you'll want to be sure to thoroughly clean the area by washing it with a solution of TSP (tri-sodium-phosphate) and warm water. Let the area dry for at least 24 hours before staining. Once you've chosen your stain of choice, you can either go right to staining the entire area (well, the stairs, I mean), or you can do a test patch on a hard to notice area to make certain you'll like the results. After that, just be sure to stain the area -- using either one (I prefer two) coats of stain. Let dry and you're done! Good luck!

If the treads and risers are plywood, it's most likely part of the "rough framing" and was meant to be covered by a finish material (carpet). Odds are the plywood is construction grade and there are visible voids, cuts, and gaps into the framing below. If you leave it as is, you'll probably find that plywood will start to break down at the front edge of the treads, and snag socks, dress hems, etc. If the goal is wooden steps, you've got a couple options. ##OPTION ONE## If the existing plywood is presentable, you can attach piece of wood to the front of each step to create a solid wood "tread nose". Using your choice of 1"x2" lumber- (use a hardwood - oak, maple, mahogony, etc). With the board laying "flat", use a sander or router to slightly round both top edges. Cut to length to match your steps (measure each step first, with rough framing, you may find a 1/4" inch or more variation from step to step). Using wood glue and finish nails, attach the pieces to the front of each step, with the board "on edge" so that the 2" face is against the face of the riser, and the top flush with the top of the tread - rounded edge facing out. If the tread of the existing steps overhang the rise, you'll need to either (a)cut the tread flush with the riser; (b)attach a piece of scrap wood under the overhang to support the new tread nose; (c)rabbet (an L-shaped notch cut with a router or table saw) the back of the tread nose to allow for the overhang. Stain and urethane and you're done. Cost - $3-4/step, depending on the wood you use. ##OPTION TWO## For another $30-50, you could cover the plywood entirely with wood laminate flooring. If using non-solidwood flooring, use a construction adhesive to glue the laminate to the plywood. Install the tread nose piece before installing the laminate to the riser, so the tread nose is attached to the plywood (glue won't bond well to the face of the laminate). ##OPTION THREE## If you want to get really fancy, matching hardwood tread nosing is available from some laminate flooring mfg's, and will give you the appearance of a professionally built stair with projecting bullnosed tread noses. However, these milled tread noses run about $15-30 PER STEP. On the upside, using the pre-made tread noses, you could do the project with nothing more than a hammer and saw (preferably a miter box). ##SAFETY NOTE## If you stain/urethane the plywood, ask at the paint counter for an anti-slip additive for painted floors. It's basically a superfine sand and gives the finished surface a slight "tooth". If you use one of the plastic-like laminates, be aware that they're very slick in socked feet. I would install the tread nose slightly higher than the surface of the tread so that the edge would give some traction if your foot slips.