Fernando said:The meaning in Spanish of "entrar en una sociedad" is to take a given percentage in their equity.
It usually refers to an important stake. I would not say "Entré en el capital de ITT con 100 euros", but it is not assumed you take a control stake.
In Spanish is quite often (1,700 entries in Google). As an example:
"Gas Natural podría entrar en el capital de Gaz de France"