I think of pressure
cookers as smaller with a single handle, looks like a sauce pan, used for making everyday meals and pressure
canners as the larger, kettle-size pots. Not sure if that's the official definition, but web stores seem to follow the distinction.
I'm not a canning expert, but I think the smaller cookers can be used for pressure canning as long as the
process is followed. Most canning recipes say to "...vent at full steam for xx minutes, then close the vent. Start the cooking time when the pressure reaches xx psi, maintain xx pressure for xx minutes..." Once you've maintained the recommended pressure for the recommended time, the food is safe.
Definitely follow tested recipes. Pressure canning, especially vegetables and meat, is not something to guess around with.
Here's a good website that has both types of canners.
http://www.pressurecooker-outlet.com/index.htm
and the Ball canning site, an excellent resource!
http://www.freshpreserving.com/home.aspx
university extensions services also have good canning info-
http://extension.usu.edu/utah/htm/fcs/food-preservation-canning/