Paul
Will this result in all packages being updated through the deb
repository rather than the Ubuntu repository?
Or does the "sid" bit restrict it to the Lyx files.
No, SID doesn't restrict it to LyX, and you're right in not wanting to
update other stuff from there. The trick is to enable the Debian SID
repository (it will automatically be enabled when you first enter it),
use Synaptic to install LyX (ignoring any messages to the effect that
you have updates for 2,387 packages available), then go back into
Sources (or Settings -> Repositories from within Synaptic) and disable
the mirror (but leave it defined, in case you need it again). If the
"you have updates" bug is still displaying, use the Reload button in
Synaptic to refresh the package list.
Thanks again :-)
Graham