Yes this is possible, I used to have an m-audio Delta 1010LT card in my PC and with this I was running my main zone (Via the SPDIF) and 3 other zones (Via the analogue outputs on the card).
All zones were controlled via MC on the PC, in my case using software called Netremote, but now there is a web interface to MC so you could control it from your iPhone or Win Mobile phone if you wanted!
You could also have uPnP or DLNA devices in different rooms all loading their music from the MC Library Server, and each devices can have their own views/menu structure defined on the server the way you want.. which is what I have now in the kids rooms. Their audio menu only shows their music so they can find it easily.
Depending on your house layout and existing wiring, DLNA boxes may work out better than running audio feeds from the PC to each room as these boxes only need a network connection, which could be wireless if needed.
If you want to run all the zones from the PC, then in terms of hardware required to run multiple zones, an audio card with multiple outputs is ideal, but you can also use the onboard audio plus an audio card or two if you prefer.
No doubt others will give you their experiences during the course of the day, but I hope this helps,
Richard