There is nothing like compatibility; unless you are Windows Home Server, then well...you just don't need it.
According to reports on the internet Windows Home Server is not compatible with Linux or Mac systems on your network. Systems such as remote backup, remote file sharing and monitoring are simply not available to MAC and Linux users at this time.
Maybe MS will add something in later, but I just can't see it with the "I'm a PC" ads out there.
Read more here
However if you have Linux systems in your house or anything fruit flavoured you might as well forget it.
Microsoft is also making WHS available for free to software developers who subscribe to its MSDN or Technet networks. This is so that developers will write software add-ons for the thing.
Not included in Power Pack 2 is the ability to do automated backup and monitoring of Mac OS and Linux PCs in the network.