Hi May
My top recommendation would be the Logitech Squeezebox series of music players,
Transporter & Squeezebox Wireless Network Music Players - Every room deserves a soundtrack
These music players will stream music from a computer (the SlimServer software that organises the music will work on Windows, Mac and Linux) and will also play music from internet radio stations too. They'll play most digital music formats, including MP3, WMA, etc, and even some more esoteric ones such as FLAC and Ogg Vorbis, although they won't play files with Digital Rights Management (DRM), but DRM is evil anyway!
They'll work over a wireless network too, so you won't need lots of Ethernet cables cluttering the place.
If you've already got a computer that you can use for storing music, this could turn out to be quite a cost-effective solution, as the software is free to download, and the players themselves are not horrendously expensive either (apart from the "Transporter" which costs over a grand and is intended for complete hi-fi buffs and audio geeks like me lol).
You've also got a choice of playing different music on each player, or synchronising players with each other so they play the same music; and you can have any mix of the two as well, e.g. 3 players synchronised playing the same music, plus another player playing different music, and another one playing something completely different too...
For a room which doesn't have an existing sound system, I'd go for the Squeezebox Boom,
Logitech Squeezebox Boom - Misco.co.uk - this has its own built-in speakers and costs just under £180.
Alternatively, if you've already got a sound system in a room that has a line-level input on phono connectors (e.g. an "aux" input), then the cheapest option would be the Squeezebox Receiver,
Logitech Squeezebox Duet Receiver - Broadbandstuff.co.uk - which you can pick up for less than £100 (this doesn't have a remote control, so you'll have to control it from the central computer, so this would be best suited for rooms where you just want some nice ambient background music and won't want to change the music much).
And if you've got an existing sound system, but you do want to be able to change the music from in there, then the standard Squeezebox is probably the best bet,
Logitech Squeezebox 3 Wireless Music Player - Broadbandstuff.co.uk - it costs an extra £50 but comes with a fluorescent display and a remote control - so would be a good choice for rooms in which the therapist wants specific music for a particular treatment or client.
Hope that helps. By the way, I've not got shares in Logitech, I'm just a big fan of their Squeezebox products, as they are what I use at home and they sound fab!