I'm currently running Windows Media Services through a Windows 2000 Media Server -- it gives you the option to stream through HTTP (port 80) which is probably why you are able to listen to Windows Media and are having problems with Shoutcast.
Check to make sure that you aren't behind a firewall, as that may disallow the ports that Shoutcast is using.
What we're doing is running our playlists with Winamp, then piping that into the Windows Media Encoder, which gets sent via Unicast to the Streaming Server, which has both a unicast and multicast streams for Off-Site and Intranet access respectively.
Winamp is a pain for dealing with playlists -- ie. we can't manage them dynamically

Ah well...dunno if I answered your question...
Cheers --
CFSM - Radio Saint Marys -
http://cfsm.stmarys.ca/