Can a microwave effect streaming?

yes, my microwave can cause my air port express running airtunes to cut out. It also causes my Xm radio to cut out as well.

You bet, probably the best way to disrupt wireless.

And water tanks, pipes and some older cordless phones.

yeah it can. That is why I ran ethernet cable in my house.

Yes, my microwave oven affects my wireless network (G), disrupting my connection on my powerbook. It's becuase microwaves operate ~2.45Ghz, very near the frequency of wi-fi. See: http://en.wikipedia.org/wiki/Microwave_ovens

Many routers have an option to help with interference from Microwave ovens or cordless phones. On the Airport Extreme this is under "Wireless" -> "Wireless Options and is called "Use interface robustness". I believe what it mostly does is to change the timeout intervals for retransmission if a collision occurs (because your microwave is shouting). The standard collision backoff mechanism interacts badly with microwave output timing or some such. Anyway, you might try turning this on and seeing if it helps.