Known users from DebianScience listed in parenthesis.
Conference tools already packaged in Debian
You may find the UK TUG FAQ answer on slides helpful.
This discussion on the mailing list http://lists.debian.org/debian-science/2008/05/msg00158.html contains a number of alternatives (which should ultimately be listed here).
a0poster (part of texlive-latex-extra) Support for designing posters on large paper.
textpos (part of texlive-latex-extra) Place boxes at absolute positions.
You may find the UK TUG FAQ answer on posters helpful.
Scribus Open Source Desktop Page Layout
Inscape vector-based drawing program. Inkscape loads and saves a subset of the SVG (Scalable Vector Graphics) format, a standard maintained by the WWW consortium.
Conference tools that could be considered for inclusion in Debian