Oh, sorry... I thought the terms were well known.
SteamPunk... is a branch of Science Fiction, where the world uses mostly steam power...
Often in SteamPunk themed media, there is often use of large pipes around towns, buildings and so fourth...
Examples:
In the latest series of .hack// G.U. "The World R:2" uses SteamPunk as a base for the in-game portion of the game.
Though I haven't seen it yet, "Steam Boy" the anime movie, seems to revolve around SteamPunk.
CyberPunk... On the other hand, jumps into the future, where technology is truly superior to just about everything.
Sometimes it even takes place inside a computer system...
Some good examples of CyberPunk are:
The movie Tron (Also featured as a world in Kingdom Hearts 2)
the "New" Star Wars Trilogy (movies 1-3)
The Matrix movies, revolve around CyberPunk. (An example of being in a computer system as well...)
The .hack// series is an interesting take on CyberPunk.