Hi There,
Checking sourceforge, apparently the project is unmaintained since mid 2005. (last release)
This is also confirmed on the bug tracker: "There is no maintainer for 3ddesktop. This means that this package no longer exists (or never existed)."
And since unmaintained software is afaik removed from the repository you'll have to build from source (although you'll probably run into incompatibilities) or get an appropriate alternative for your desktop environment.