Hey mate :)
Well, apparently there's a Treaty of Linguistic Union between nederlands and flaams, which agrees that any new changes in one language will be adapted by the other. That is, Dutch=Flemish. However, there are a couple of pronunciation differences, eg. the fricative G in nederlands is more like a Y in flaams. And some contractions, eg. ik->'k, and het->'t
In practice, there's a lot less similarity. :) There's a bunch of Flemish dialects spread across north Belgium, so the big question is which one do you want to focus on? The speech of Brugge (Westflaams) is different to that of Antwerp ('t Limburgs).
One lovely thing I found about Antwerp is that they would rather you tried speaking the local dialect - or at least basic nederlands - instead of English. Brugge is more a tourist destination so they tolerate English more kindly.
Good info on Flemish dialects is scarce but here's a lovely little site I found whilst looking for info on Westflaams: www.lowlands-l.net
Good luck - it's a lovely piece of the world! ^^