Can't log in to Xubuntu 9.04 Jaunty

[Dave M G]

Ubuntu users,

On my laptop, which has been running Xubuntu since 8.04, I just 
installed Jaunty.

The installation went without a single error message.

However, on first boot, the login interface is over-sized in such a way 
so that only the top left quarter or eighth fills the entire screen. 
That makes it impossible to see most of the interface and I can't log in.

How can I get the login interface to scale properly to my screen size so 
that I can log in?

Any advice appreciated.

-- 
Dave M G