Can anyone tell me the differences between a legal seperation and a divorce? (besides the obvious)?

I would prefer an answer from a legal point of view. I need to know the differences so I can file the correct papers. Also, if I do choose a legal seperation, how do I go about having my spouse removed from the apt. we share? the apt is a condition of my employment. Also, i need information on Spousal support, when is a spouse eligible and not eligible for spousal support? Also, since i am on a limited budget, can anyone tell me which papers to file? I alreasy have the basics but i just want to make sure i cover my butt because my spouse has access to free legal help from a top notch lawyer firm and i dont. Also i just found out I am pregnant. Do i have to tell my spouse and include an unborn child on the legal paperwork? What happens to me if i dont list the unborn child?