OK, I figured it out. For some reason, my other users had problems with 
~/.xinitrc and ~/.xsession files on session startup. When I renamed BOTH of 
these for the affected users, everything appeared to return to normal.

So now I'm left with a SuSE mystery: Why were the root and my normal user 
account unaffected? I log in as a user to do updates, and as root on 
occasion for maintenance, so perhaps it's related.

In any case, I suspect that the unsuccessful install of wdm is screwing up 
the setting of $WINDOWMANAGER that both of these (.xinitrc & .xsession) 
look for. They both exist by default in /etc/skel, so I'm assuming wdm was 
the culprit.

I obviously need to get more familiar with the X startup flow. Having 
mastered bash login script flow and init scripts, I suppose it's 
going to be similar. Anyone got a good pointer to X startup info?

- Bob