I'm really interested of learing Tamil. I want to know how long it would take and some tips.?

And as well as i need to know some guidelines... I already know very basic things in Tamil, but i need to learn SPOKEN language(for the time being only SPOKEN). I speak Sinhala as my native language, I'm a social worker and I've to work in areas like Jaffna and Eastern province in Sri Lanka (For schools). And i've heard Jaffna tamil, eastern tamil and indian tamil stuff are different. Most of the Tamil learning resources (Internet resouces, movies) are Indian Tamil. So is it worth to follow those resources to learn Sri Lankan Tamil?? (Since I've to keep ociate with children, i must know the way they speak)