What all do you need?
You can have anywhere from 1 to 32 zone players (a mix of current amplified ZP120, non-amplified ZP90, or the older models ZP100 and ZP80). I currently have 5 (bedroom, living room, kitchen, media room and nursery) but was running only 2 for my first year and it was awesome. Each zone can be linked to any or all other zones in 100% perfect sync (something that software based music systems cannot truly do) or each play their own source (a few playing music off your computer or NAS and perhaps a few playing internet sources such as pandora, napster, rhapsody or various internet radio streams).
Anyways, if you want more detail on that, that's fine...but the long story short is that as soon as you have at least 1 zone player running, you just need to tell it what to do. You can use the free controllers for your desktop or the free iphone/ipod touch app or you can use a Sonos controller. The CR200 is the brand new one and is really smooth. It talks directly to the sonos zones (which are likely spread around your house) so its likely to have a high signal anywhere and be crazy fast to connect and be ready for use. the "free" versions I mentioned connect through your router. You can use any combination as well, and again using my personal example, I have an actual sonos controller for the main level and for others to use (and to always know where it is) but use my i-touch as well as I generally move around. I do have the desktop controller available and occasionally if I'm at my desk and too lazy to go get the sonos controller its nice to just pull up the program and control any of the zones that way too.