You can stream audio AND video from your home server to your iPhone right now with no additional software. You won't have playlists, but for selection of specific songs or videos it works great...
System Preferences > Sharing > turn on Web Sharing
In Terminal, navigate to the web directory:
cd /Library/Webserver/Documents/
And make a symbolic link to your music or video location:
ln -s ~/Music
ln -s ~/Movies
Then put in the IP of that machine into Safari on the iPhone:
http://192.168.1.100/Music
http://192.168.1.100/Movies
(Replacing the IP number above with your dekstop's IP.) And there you have your files.
Interestingly, I can play MPEG-4 video files through this connection that iTunes won't let me sync to the iPhone directly. So it seems iTunes is more restrictive than it needs to be.