Where's my desktop? (Linux)

In a misguided effort to get apt-get to install some package, I
unwisely uninstalled and re-installed several gnome-related packages.
The re-installation went (seemingly) without a hitch, but now a
few things are very messed up.

The most serious one is that when I run startx from the console,
I get an X environment *with no desktop*: the background is a
fine-grained black-and-white (effectively gray) herringbone pattern,
not the solid-color background I had before, and there are no bars
with launch icons, minimized windows, etc. running along the bottom
and top.

(Luckily there were a few xterms in an earlier saved session, which
got re-started automatically for the new X session, otherwise I
don't know how I would have been able to communicate with the
system--other than by switching to a text-mode console with
ctrl-alt-F? or by killing the X server altogether with ctrl-alt-backspace.)

As before, I have chosen gdm as my default "display manager", but
this does not seem to be enough to bring back my desktop. If
instead of running startx from the console I run gdm, eventually
(after logging in again) I land at another desktop-less X environment,
although this time I get my old solid-color background.

What must I do to bring back my old desktop or ANY desktop?

Thanks!

kj

P.S. I am running Linux Debian 3.0 (woody), with a 2.4.18 kernel.

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NOTE: In my address everything before the period is backwards.