Ok, I want to make a war tortoise that is really big (700-800 lbs?) rather slow, and can be trained to fight and is obviously tamable and purchasable on embark (is this part possible?).
Other than that is it possible to say in DF where a creatures parts are? I.e. The tortoise has all of it's organs and it's body etc... in a shell to protect it with just a little bit of the feet and head sticking out.
I'll answer what I can offhand, yes all of this is easily possible with the raws.
df.magamawiki.com will be the best thing you have, as well as the ingame raws.
http://df.magmawiki.com/index.php/DF2010:Creature_tokensOf those you mentioned.
[BODY_SIZE:X:Y:Z] describes the weight of your creature. X is Years, Y is Days, and Z is the weight. 1000 is approximately 1 kg. So..
[BODY_SIZE:0:0:1000] Means that your creature would weigh 1 kg on birth.
[BODY_SIZE:2:0:10000] Means that your creature would weigh 10 kg at 2 years of age.
[BODY_SIZE:100:0:2000000] Means that your creature would weigh 2000 kg at 100 years of age. etc..
All Training is done at the Kennels and will always say Train War Dog, and you won't get to choose which species if you have multiple trainable species.
[TRAINABLE_HUNTING] Will allow your creature to be trained to Hunt
[TRAINABLE_WAR] Will allow you to train your creature to really Fight
[TRAINABLE] Allows both.
You need these in order to be allowed to purchase on embark as a Pet.
[COMMON_DOMESTIC][PET]
Body Parts themselves are determined by the [BODY:X:X:X] with any number of body parts. You will also need to define tissues and such, I suggest taking the default Turtle bodyparts and tissues to get what you want right now.