You need to examine scripting...or a scripting helper...
The scripting tools let you define camera, sun and cloud positions.
If I remember correctly there are basic instructions included with the application.
You can also use tools like campath
http://www2.cs.uh.edu/~somalley/campath.html and terranim (available at Ashundar
http://www.ashundar.com/ I believe) to set up scripts that can then be used to generate the frame sequences for an animation.
The frame sequence is a collection of renderings that are numbered sequentially.
You will need a program to compile the resulting frame sequence into a movie file. VirtualDub
http://www.virtualdub.org/ is a free application that lets you achieve this, and Quick Time Pro (from Apple) is a relatively cheap commercial application that will also turn a frame sequence into a movie.
Doing this with tg 0.9 is relatively easy...and depending upon your settings and the nature of the landscape, (water can really slow things down !) not too time consuming providing you have a reasonably fast machine.
It's not difficult in tg2 (tgtp) as long as you have the deep + animation version. It's manual and keyframe based. The render times are currently fairly long in tgtp ...so any reasonable quality animation would most likely take quite a while to render.
Hope this helps..
Regards
Chris