'sounds like you have way too many customs sounds.'
That is the only thing I can think of in making a trailer that big in file size. Try using more in game music and sounds, at least to get it to about 1 mb. If you still have custom sounds and music, make sure they're encoded at about 92 instead of 128 or higher as mp3's.
I agree with the spyware, or interenet protection program comment. These programs that are supposed to protect you from getting things off the internet also prevents you from getting things on it.