How many Rooms and Sources?
If you want to listen to one source (ex. computer audio) in up to two rooms at the same time, you can use the A/B switch on your amplifier/Receiver to switch speakers.
If you want the same source in 2 or more rooms at the same time, you will need to include some kind of switching device (options include anything from cheap radio shack equipment to high end professional types that are available at specialized shops).
Depending on how many rooms you want to listen to at the same time, you may have to have aditional amplification for additional rooms, as setting up more than one pair of speakers on the same speaker posts on your amplifier/receiver may cause damage to the amp. Simple switching devices will only let you switch one alternate room at a time to avoid this problem.
If you want more than one source to be played at the same time in different rooms (ex. radio in one room, CD in another) you can consider receivers that have a multiple zone function, such as Marantz SR5500 (first option on my mind, i am sure you can find many others with the same or better functionality)
Finally, if you want to be able to control different sources, playing in different rooms, from each of those rooms you can consider different options, from a remote control extender to complex custom instalations. I would reccomend going to a specialist for this last option, as the equipment is expensive and may require professional instalation.
hope this helps.