Dapper upgrade hangs - what to do?

[jean-ooo at taming-openoffice-org.com]

Last night I started the upgrade process from Breezy to Dapper, using 
the Update Manager. At the point where it was downloading files and 
saying "3 hours to go", I left it to run overnight. When I came out 
this morning, there was a dialog box on the screen with the title 
"Debconf on [name of my machine]" and the heading "Postfix 
Configuration". I clicked Help, read what it said, closed Help, chose 
"Internet", clicked Next. On the next screen (where it asks for host 
etc), I decided I should have selected "No configuration" so I clicked 
Back. It did not go back, and after that, I could not do anything on 
that dialog.

So I opened the window labelled "Upgrading Ubuntu" to see what point 
the upgrade had reached. It was at the "Downloading and installing the 
upgrades" step, and the "Applying Changes" indicator is going back and 
forth", but nothing seems to be happening In the "Terminal" part of 
that window it says:

Extracting templates from packages: 100%
Preconfiguring packages ...
Moving /etc/cups/cupsd-browsing.conf to new location 
/etc/cups/cups.d/brows.conf...

This message has been sitting there for over an hour (and could have 
been there most of the night, for all I know).

The system does work -- I am using Firefox to send this message and the 
ethernet connection is obviously working. But I don't know what to do 
next. Can I safely cancel the process? I sure don't want to hose 
anything serious.

FWIW: this is a Dell Inspiron 510m laptop, dual-boot WinXP Pro/Ubuntu 
5.10. I keep my data in a shared drive (as well as backed up elsewhere).

Thank you for any suggestions.

--Jean