First go here, http://www.sane-project.org/ and see if your scanner is
supported

(http://www.sane-project.org/sane-mfgs.html#Z-MICROTEK)

If it is supported you can acces your scanner through Sane (you might have to
install it though synaptic)

If it isn't supported (and I don't see a i800 in there) you need to check the
manufacurers site for modules.