Any DLNA capabable software (like VLC) should be able to do this. iTunes seems to be lacking this capability.

Hey! I'm running an old laptop as a media server and using Media Monkey to handle the audio, it's great cuz I can stream to my Xbox 360 for music playback in-game and such! My mac is what's connected to my best speakers though. Is there a way to stream audio from the Media Monkey server to the mac? and if so, what program(s) do I need to stream it? I would hope to be able to poke around the library like you can on the Xbox 360, too.