http://support.apple.com/kb/ht1846quote: These Macs can use 64-bit editions of Windows Vista and Windows 7 Home Premium, Windows 7 Professional, or Windows 7 Ultimate:
MacBook Pro (13-inch, Mid 2009) and later
MacBook Pro (15-inch, Early 2008) and later
MacBook Pro (17-inch, Early 2008) and later
Mac Pro (Early 2008) and later
iMac (21.5 inch, Late 2009)
iMac (27-inch, Late 2009)
iMac (27-inch, Quad Core, Late 2009)
MacBook (13-inch, Late 2009) and later
iMac (21.5-inch, Mid 2010)
iMac (27-inch, Mid 2010)
Mac mini (Mid 2010)