auto login

I got autologin on Centos (KDE) working OK.
Problem is, after you log off, it waits 30 seconds
and then logs the user back on again.

What I would like to do instead I think is have a login,
"demo", that they could log in with.  Problem is, all
logins require a password.  I would like them just to
be able to type "demo" in the login prompt and it will
log them in without them having to enter a password, and
will run my program automatically.

I know how to do all of that except remove the password
requirement (obviously for user demo only).

Anyone know how to do this?

Tony