Two possibilities -- either Win2008 won't allow access to the NIC driver that is needed, or the firewall won't let the packet out.
You might be able to use Wireshark from a workstation to watch for the Magic Packet. Here's what you're looking for:
http://en.wikipedia.org/wiki/Wake-on-LANIf you do NOT see it coming out, and you've disabled the firewalls & such, then it may be necessary to check with Microsoft to see if they have removed the capability of directly sending packets from the more secure x64 environment. Would be interesting to also check a VM running inside the x64 OS to see if THAT can send the packet...