(OK, if this is still up so high in Google, better add something ...)
There are a whole lot of sites on the Internet that will help you learn how to read it, but for a fee.
But I did manage to find places for it for free.
A woman affiliated with the Israeli Masorti movement reading the trope (she also has reading of the actual megillah)
Beverly Hills Chabad has scans of a tikkun with the Megillah (i.e. both with trope and vowels and in the form it appears on the actuall scroll). They also have audio files, but I would NOT recommend learning to read from them.
For one, they're reading with the Ashkenazi-on-steroids pronunciation that the Lubavitchers (and perhaps all Hasidim; I'm pretty sure misnagdim are more straight-up Ashkenazi pronunciation that a lot of our fathers/grandfathers/great-grandfathers even used in their shuls [assuming they weren't Hasidim]). Not just the Ashkenazi pronunication of ת without dagesh (i.e. sov) and of kamatz as aw, but multiple crazy-ass pronunciations of holam as well.
But more importantly, they're reading for real, and thus (as is the tradition) extremely fast. Instead, I'd use Kolel: The Adult Centre for Liberal Jewish Learning:
the guy reading is a baal kore at a Conservative shul in Toronto, so it's perfect for me; however, the trope is as far as I can tell the same as what the Lubavitchers are reading.
If you cannot deal with either the Lubavitcher or the Conservative version, you could try the Cantor Pinchas Rabinovicz version. He is affiliated with Aish, and his pronunciation is pretty hard-core Ashkenazic (though not quite the steroids version of the Lubavitchers), but he does read it nice and slowly, making it ideal for learning to read.