The big problem here is licensing. If you're playing music you wrote, produced, and recorded, there won't be an issue. But if you're playing music from ripped CDs, even if you bought it legitimately, any distribution as you describe will be illegal.
Because this is a company and you're playing or making the music available for several people, this counts as broadcasting and you need a special license for any sort of distribution system.
If word gets out that you're hosting a media server and playing music for people inside your office, count on the RIAA to come down on you with a whole boatload of legal badness.
An easier solution would be to allow people to bring their own portable media players and then set reasonable rules regarding sound levels/headphones/internet radio/etc.
Here's a link with info on what constitutes a "public performance" when it comes to music and some of the considerations necessary regarding licensing of such things: http://www.ascap.com/licensing/licensingfaq.aspx
The important bit is perhaps the description of "public performance":
A public performance is one that occurs either in a public place or any place where people gather (other than a small circle of a family or its social acquaintances.) A public performance is also one that is transmitted to the public; for example, radio or television broadcasts, music-on-hold, cable television, and by the internet. Generally, those who publicly perform music obtain permission from the owner of the music or his representative. However, there are a few limited exceptions, (called "exemptions") to this rule. Permission is not required for music played or sung as part of a worship service unless that service is transmitted beyond where it takes place (for example, a radio or television broadcast). Performances as part of face to face teaching activity at a non-profit educational institutions are also exempt.
Don't get me wrong: I think the music publishers (RIAA and their member companies) are a bunch of greedy pigs who've cornered the market eradicating any reasonable sense of fair-use and eliminating most of the benefit musicians and artists should derive from their music. The issue here is current legality, not personal preference. To play music or to enable others to play your music in a public place, such as an office, requires a specific sort of license that costs some pretty good money.