I went through these questions myself a couple of years ago. I have a BS in Pharmacy, and wanted to study towards a MS in CS. I wasn't sure what sort of transition this would be, and how much 'remedial' work I'd have to do before starting on the MS.
It turned out to not be so bad as expected. I surpassed the math requirements from what I had taken in my undergraduate work. Before being admitted to the MS program in my particular school, I had to complete intro programming (C), advanced programming (C++), data structures, compiler theory, and operating systems. I believe this is all, if memory serves me correctly.
Although I am still working towards the MS now, I am still working as a Pharmacist, due to the employment downturns. I enjoy the studies, and want to make it my future line of employment, but haven't felt strongly compelled to make the jump into seeking work yet.