How would you find out what harpoints an object has? The reason I want to do this is I'm trying to find out the hardpoints on a republic trooper so I can attach a light to one of them.
[if you know of any please list them]

You could search and find the answer HERE
You can personally find them out using a program called Unwrap3D or by searching through the file in a hex editor, as mentioned in the thread linked to above.

Ok thanks! but what would you put in your odf if you were attaching another odf to it?
AttachOdf = "***"
AttachToBone = "***" ?

it better to give an unit a damageffect that starts at 0% and stops at 100% damage thats the easyest way to attach an effect to an unit, look in the droid odfs for reference

Which would work dandy, except that he's trying to add a light, not an effect. Look in the Modelling FAQ topic about addon meshes, it has a sample ODF code at the bottom.