You can choose to use any programme to create your poster. I recommend powerpoint - it is more flexible than word, and allows for layering like publisher - 2007 has really cool features.

Examples
Technology -
Social Sciences
Health -
PE -

Todays Task

Create a placemat about yourself. Making placemats at the start of the year is a great way of getting to know your class. They can be printed and enlarged to A3 and then laminated. These are then great on tables/desks to show where children sit and for children to work on.
My example -
Placemat.jpg

Tip sheets
Powerpoint 2007 quick guide - http://www.customguide.com/pdf/powerpoint-quick-reference-2007.pdf
How to copy images off the internet - http://www.d.umn.edu/~hrallis/guides/SampleImages/SampleImagesGuide.html
Working with Images in PP 2007 - http://www.uwec.edu/help/PPoint07/image.htm
Instructions on how to insert an image as a background
Introduction to Powerpoint 2007

Important
Save your poster as a pdf to email http://presentationsoft.about.com/od/powerpoint2007tips/ss/07saveasPDF.htm