Ideally, in the South -
dw i'n moyn– I want
ma eisiau i fi – I need to
(from the SSiW Challenge 1, Vocab text)
However, as in English, dialects are somewhat interchangeable. So, regarding your question "can eisiau mean want?" - if I was to hear "dw i'n eisiau", I would personally take it as "I want".
Now I can't get that Meatloaf song out of my head.