I want to find a program that had the same features as SnagIT from
techsmith. I am aware of the various Linux basic screen shotting
programs (Imagemagic 'import', GIMP, Ksnapshot etc.) but I really need
a program that will let me do 'full page' screenshots of websites ie.
a scrollable image of the site as the web browser would see it.

See that product here:
http://www.techsmith.com/products/snagit/tour/capture.asp and then
look down to 'Scrolling Window Capture'

Open source would be preferred, but I am willing to look at commerical alternatives.