I have been with the same employer for the past one and half year. At the beginning I was full-time and salaried. Then I started school so became part time (32 hours or so) and got paid by hour. Now, I am 4months pregnant, and was told that I will be given STD by my company. I wonder - the length of STD will depend on my status as fulltime or parttime? Will the benefits be impacted by my status? Is STD the same thing as materntiy leave?

No, STD is not the same thing as maternity leave, although they may happen at the same time.

STD is income replacement. It is not leave time of any sort. STD is what pays you when you are on a qualifying medical leave; it is not the leave itself.

What you are eligible for will depend entirely on the terms of the disabilty policy. The law does not dictate (in your state anyway) what disabiltiy benefits are available to full time vs. part time employees. It's a contractual, not a legal, issue.