Budget? Because "simplest" and "entry level" could mean basic, cheap, but complicated to setup and use, or it could mean easy to setup and use, but more expensive to buy. If the latter ,and he can afford ~$1500, take a look at Sonos:
www.sonos.com/default.aspx
Instead of having a system in each room and/or running speaker wire to other zones, Sonos does everything wirelessly. It will play his personal MP3 collection, plus internet radio, and the Napster, Rhapsody, Last.FM, Sirius and/or Pandora online services. It is expandable up to 32 zones of music, you can have different music playing in each zone; or the same music, perfectly synchronized, playing in multiple zones.
As far as setup and use is concerned, I setup my first 2 zones in less time than it took to unpack the boxes, and the remote is so intuitive, even my tech-illiterate mother was able to play music the first time she picked it up. Huge WAF among Sonos fans. It is a bit costly, but it is far less expensive than installer provided multi-zone audio that can cost 10's of thousands and requires wiring throughout the house. For me, it is the single greatest electronics purchase I've ever bought, simply because it made me rediscover my love of music, which had severely lapsed during the CD->MP3 era.
