I have OS X mountain lion 10.8.3, with jdk 7 v7 installed.
I downloaded Pentaho BI server CE v4.8

When I launch it via terminal and visit localhost:8080, I see that tomcat has started but the page says
HTTP Status 404 -

type Status report
description The requested resource () is not available.

I've been able to get it working on archlinux and Windows server 2003 the same way.
I have to say that I'm a complete beginner. The error indicates a JDBC connection error ... I don't have a database running on OS X yet, but I thought that would need pentaho running and then add a connection. This is what I recall doing on windows.

I'm also struggling to find installation instructions.

The pentaho log says

1 2013-07-14 18:03:35,491 ERROR [org.hibernate.util.JDBCExceptionReporter] java.net.ConnectException: Connection refused
2 2013-07-14 18:03:35,562 ERROR [org.springframework.web.context.ContextLoader ] Context initialization failed