You've actually gotten colder, compared to your original post. This is also a linear first order inhomogeneous ode and can be solved by various means, i personally opted for finding an integrating factor, for both this equation and for the other equation in the Runge-Kutta thread. I need to sleep now but you should be able to find all the details you need to find the solution at, Integrating Factor -- from Wolfram MathWorld .
EDIT: Well don't i feel silly, should have pointed you here first, http://www.mathhelpforum.com/math-he...ial-38182.html .