It seems a number of installation errors have to do with DB connection error. Thought I would share my experience and one suggestion here.
During installation, I got this db error "Error establishing a database connection", which also listed three possible causes. I made sure i have correct userid/pwd, correct hostname, and my db is running. But it turns out that the real culprit is: I have a newer MySQL instance (4.1.7) that is incompatible with php_mysql module - "Client does not support authentication protocol requested by server". So I have to follow the instructions here to work around my problem.
So my suggestion is: in addition to display the three possible reasons, would it make sense to display the real error msg returned by MySQL server?