I am an H1B holder from a FInancial Institution in Boston and I was wondering if I can open a small business with one of my cousins who has a GC.. and register it legally. I want to open a Nepali Resturant since I have a lot of experience in the field. I know my cousin can start a business but I want to be a 50% partner (not just by word of mouth, but in papers as well)... but since I am on a visa, I am not sure if I am legally allowed to invest in a resturant.

Serious and knowledgable suggestions only please.

Which section of law restricts you to become a businessman or invest in this country?  People spread these types of wrong information have just miserably failed in their life and they are spreading wrong information just like Nepali Netas. Entrepreneurship is a skill and anyone who has this skill should feel blessed. 

You cannot work for a different company while under H-1B for one, but you can certainly invest claiming to be a passive investor (i.e. you aren't working at the restaurant).

 Thanks for the suggestions guys!