Can i catch sinusitis from someone with the condition?

Generally no: A sinus infection is bacterial and is usually preceded by a viral upper respiratory infection (which is contagious) or by allergy (not contagious). Many of the organisms that cause a sinus infection are naturally present in the environment but given the right conditions... Lead to an infection.

Not neccesarily: You can catch a virus or bacterial infection if the person with developed sinusitis from an underlying infection. You will not catch a sinus infection from some one else directly.