Steampunk broke off from cyberpunk in the 1980's. Steampunk touches many areas including but not limited too science fiction, alternate history, speculative fiction, Victorian era, steam power, anachronistic technology, gaslight romance, and Mad Scientists!
The genre and culture is due to its involvement within a world where steam power is the primary source of energy, hence, Steampunk. Although, the steam power ear is usually in the 19th century it does more often then not have futuristic technology. *Rubs hands together evilly* This is were you can picture the Mad Scientist in her laboratory creating dirigibles, parasols that spray poisonous gas, and corsets that don't pinch.
Cyberpunk and Steampunk are closely related and influence each other a great deal. Lets just say that the biggest difference that distinguishes the two would be that Steampunk tends to have less dystopian settings.
Steampunk is truly a growing movement as the concept develops. The fashion is just so becoming. It tends to take the height of Victorian fashion mixed and fused with various looks of today. Incorporate a few gears and cogs, military garb, ray guns and technology pieces. Look forward to petticoats, corsets, parasols, & goggles!
(Image from http://brassgoggles.co.uk/blog/)
A Sample of Steampunkery Links: