wrote:

I have an older home with a bathroom that has poor ventilation which
causes shower steam to coat the walls with moisture. In effect this
yields unwanted mould on the bathroom ceiling and other places like
tile grout and shower curtains. The differences between my bathroom
and a large petrie dish are begining to blur.
I have accepted the fact that I have to install an exhaust fan come
spring time
so I am begining to do a bit of research on the easiest method to
install an exhaust fan in an older home. I came accross this PDF
http://www.gov.ns.ca/energy/enerinfo/ventold.pdf which is a good start.
After reading this I realized that the most effective way to install an
exhaust fan is on an exterior wall, exhausting directly to the
outdoors. Does any one see any potential issues besides a proper way
to insulate? Looking forward to your replies.

Insulating the cold walls is where you should start.

If you install a fan, connecting it to the bathroom lights is fine. I
assume you don't spend a lot of time in the bathroom. The fan doesn't
have to run very long to get the relative humidity down to the point
where condensation won't be an issue. Ex: My bathroom is 10' x 4' by 8'
which is 320 cu ft. So, a 100 cfm fan will cut the humidity to 50% in
3 minutes.