Learning Fortran

Does anyone know how a C Programmer would go about learning Fortran, specifically Fortran 90?

I learned today that the software that my lab uses for molecular dynamics simulations is written in Fortran and if I want to do anything to make it run faster, I will need to be able to read and write Fortran.

Before anyone suggests it, there are no courses on Fortran offered by my university's computer science department, so taking a class on Fortran is not an option. I even checked the graduate courses and there are none on Fortran.