With your machine ready for C++ development, there is only a single step to prepare for ArcGIS Engine development, and that is to source the <Your Installation directory>/arcgis/engine10.0/init_engine.sh (or .csh, depending on your shell of choice). If you prefer, that can be done in your shell's RC file (.cshrc or .bashrc, for example). Otherwise, you must source that file once per shell.
To use the samples source the <Your Installation directory>/arcgis/developerkit10.0/init_devkit.sh (or .csh, depending on your shell of choice).
If you have the engine installed and registered, but you are getting the error message "Error: Could not open include file <ArcSDK.h>.", try sourcing the init_engine script.