The parts of the keyboard you can replace are the "caps" (plastic covers) on the keys, and the scissor hinges (the white things in the photos on Powerbookmedic.com.) The switches are contacts glued to rubber membranes, and can't be replaced individually.
If all you've done is spilled a sugary drink in there, you should be able to clean it by prying up the key caps and maybe the scissor hinges. This is not easy, because the fittings are very fragile (very thin plastic.) Since you're considering replacing them anyway, you might as well give it a try.
For the full-sized keys, I think the best way to pry them up is to from the side. Be very careful to to put too much pressure on them. (I've found that the half-size keys (like arrow keys and F1-F12) are just too fragile to bother with.)
Once you've pried up the cap, you'll see the scissor hinge. You should be able to tell how it works and how to pry it out. Try to remove both "leaves" of the hinge together; they tend to break if you try to pull them apart. Again, the hinges are made of thin plastic and can break easily.
First, try to clean the mechanism and the underside of the key using some rubbing alcohol and Q-Tips.
If you break one, or just can't get them clean enough, then you'll have to get a replacement from someplace like PowerBookMedic.com. Once you've pried up the old one, you should be able to see how they fit back in. It's tough, but not impossible. After you get the scissor hinge in, the cap snaps on fairly easily.