Oracle Express Edition: Third Strike
So I set that to the XE directory. And lo! the ORA-12557 error went away and the database build progressed a bit further. Not far enough to actually build the XE database you understand, but at least it was connecting to the instance. Unfortunately changing that variable to point to XE home breaks my 9i installation very badly. As I need 9i for my work right now and I don't need XE I think that just about wraps up my XE adventures for the time being.
In an unrelated item I note that the Register has a report on a survey finding that software problems cause people to swear, drink and throw things. Well I never! The things these surveys reveal!