writing on chalk board

... hmm, well, not exactly, what you want (=you still need a picture of a chalk board...):
http://www.geethree.com/slick/galleries/s6demopages/s6whiteboard2.html

Ted,

Find a graphic of a blackboard you like, import into iMovie and use try this plugin

iMovie effects by cf/x "movie canvas" $3.50
http://www.imovieplugins.com/fxhome.html

Can be found in the annotating category.

PS. Slick plugins volume 6 has a plugin called "Whiteboard", but you have to purchase the entire effects bundle for $70
http://www.geethree.com/slick/galleries/d_v6.html

Hope this helps