To install OS X Server 4.0 Developer Preview, you need one of these computers:
""iMac (Mid 2007 or newer)"
""MacBook (Late 2008 Aluminum, or Early 2009 or newer)"
""MacBook Pro (Mid/Late 2007 or newer)"
""MacBook Air (Late 2008 or newer)"
""Mac mini (Early 2009 or newer)" "
"Mac Pro (Early 2008 or newer)" "
"Xserve (Early 2009)"
So probably the same for the non-server version of Yosemite