I believe you can do this with any of the ode solvers.
One thing to note is that you need to convert the second order ODE to a system of two first order ODEs and explicitly solve for the derivative terms. For instance, the equation
a*x'' + b*x' + c*x = cos(3*pi*t) + cos(4*pi*t)
would become the two equations
x(2)' = (1/a) - b*x(2) - c*x(1) + cos(3*pi*t) + cos(4*pi*t) x(1)' = x(2)
Then, you can easily write the derivative function that the ODE solvers require:
function dx = derivs(t,x)
a = 1;
b = 1;
c = 1;
dx = zeros(2,1);
dx(1) = x(2);
dx(2) = (1/a) - b*x(2) - c*x(1) + cos(3*pi*t) + cos(4*pi*t)
