vector multiplication

I am sure this has been asked as it is the basics of vectors and matrices.
I am trying to multiply a vector (0,-1,0) which is my heading in local space initially when my character is loaded.
I like to multiply it by the 3x3 section of the object's affine 4x4 matrix.
Do i need to write these functions or are they provided.

vector3d * 3x3 matrix = new vector3d ish.

I looked at the vector and transformation files in the source but could not find the functions.
once again I am not using bullet.

any ideas.
I might be doing this all wrong to begin with.

Humm SIO2 vector operations are in C not C++... You might wanna look at btVector3 instead from Bullet.