Seattle companies who rent posterboards (includes delivery and set-up):
Triumph Expo and Events -- http://www.triumphexpo.com
GES Exposition – http://www.ges.com/contact_ges/offices_na_bu091116a.asp
Standard poster boards are 4' x 8' and they are double-sided.
The "useable" surface area of each poster board side is 3' 9" high by 7' 7" wide. (The rest of the area is taken up by the frame.)
For one poster per side, you may inform the authors that the allowable space is: 91" by 45" (or round down to 2 meters by 1 meter)
For two posters per side: each presenter may plan on an area of 45" x 45" (or round down to 1 meter by 1 meter -- with room to spare to separate each poster)