i heard that the Belgians speak French and Flemish in Brussels, Brugges and Ghent. Should I learn some French, or do they speak English well enough that I can get by speaking english??
Belgians in Brussels speak French ( or English) . Belgians in Bruges speak Flemish ( or English)
You'll find that most Belgians speak English and French and many speak Flemish as well. I don't think you'll have any language problems.
BTW, "Flemish" is a dialect of Dutch. Language politics are particularly hot in Belgium right now, so if you do try to use a little of the local language, make sure you use the right one. Most of Brussels speaks French, Bruges and Ghent use Dutch.
My wife and I were in Brussels for a lunchtime stopover in 2003.. we found that folks spoke English. But it's always nice to say hello, do you speak English, please, and thank you in the local language.
Brussels is officially bilingual but most people will speak French. Practically everyone in touristed locations will speak reasonable English, but you may need French in smaller shops and speaking some French will always be appreciated. In Brugge and Ghent almost everyone will speak English and for political reasons most people will be much more willing to speak English than French. I spent a few days in Antwerp and Ghent a couple of weeks ago and met precisely one person who was more comfortable speaking French than English. It will help to learn at least the Dutch words for Hello (tag, pronounced close to "tack"), Please (alst-oo-BLEEFT), and Thank you (dank ooo).