Does anyone remember the wonderful game Colonization? also by Sid Meier. I wonder if there is any mod that is somewhat similar for Civ4.

because of how the units work it really wouldnt be possible.
unless each unit you built removed a great person from a city, and every unit could place a great person [i.e. GP Farmer who gathers more grain.] in a city at its own expense
but would be hard to do and less fun then just playing colonisation