I agree with all of the above posts, the interactive whiteboards are very useful bits of kit. However, something worth bearing in mind is the cost of replacement lamps for the projectors. A big portion of my previous job entailed looking after 50 or so interactive whiteboards, and we were always replacing lamps. They tend to last around 1,500-2,000 hours dependant upon the projector model, and cost anywhere from £150 to £500 per lamp!
Try XMA, they were our supplier and normally gave us a good deal
http://www.xmaonline.co.uk/products.aspx?L1=AV&L2=IW
Ox
