You can find additional information on the sponsored links below on this page.
The following downloads are for the BuildCraft 3.x release, for Minecraft 1.2.3.
WARNING! This is an Alpha version of the game! It’s unfinished. There is no multiplayer, and no date for multiplayer – don’t ask for it. There will be bugs – please report only on the dedicated forum section. It’s very lightly documented – recipes are not yet published, and the official documentation does not contain anything about it. You’re trying this out at your own expense!
http://dl.dropbox.com/u/44760587/buildcraft/3.1.4/index.html
You can install SpaceToad’s buildcraft blueprints just by copyings the contents of the following zip file under your .minecraft/buildcraft/blueprints folder. It’s currently quite limited, contains only a power plant, a automatic wheat farm and a slab factory. But more is coming!
Here are some videos that should give you an idea on how that is supposed to work or be used for. Again, everything is alpha!