Physics/differential equation?

This is part of a lab we are doing and I am having some difficulty with it: Show that if a bar magnet suspended in a uniform magnetic field B is displaced slightly from its equilibrium position, it will oscillate with a period T=2pi sqrt(I/MuB) where mu is the dipole moment of the magnet and I is the moment of inertia of the bar. I can be determined by weighing and measuring the bar and realizing that I=M/12(l^2+a^2) where l and a are the length and width of the bar and m is its mass.