Public speaking scares me.. any advice?? anyone please?

i am a university student and am realy scared of speaking in front of the cl. raising my hand up and asking questions and giving my opinion just scares the hell outta me. its a fairly small cl with about 20 students but i get so frustrated that i cannot say anything in cl. i just have a fear of speaking out loud. im ok if its a few people but not the whole cl. and i'm also afraid of the lecturers/tutors. i get really shy. i need to overcome this to be a good active student.. i really wanna change. any ideas??please help. my career depends on this.