What kind of player are you using? Server-side smil file for multi-bitrate streaming works with IPhone and Silverlight. You would use a .sml extension, and the URLs would be:
IPhone
http://localhost:1935/vod/smil:myplaylist.smil/playlist.m3u8
Silverlight
http://localhost:1935/vod/smil:myplaylist.smil/manifest
See the live and video on demand tutorials, multi-bitrate section for more details.
If you are trying to do muti-bitrate streaming with Flash player, there are links in the above tutorials to an Adobe article. But be aware that it is must more complicated then multi-bitrate with IPhone and Siliverlight and might be disappointing. You might want to hold out for Flash HTTP Streaming in Flash player 10.1 and forthecoming support for that in Wowza, including multi-bitrate which should be much better. No eta, but it is upcoming on the Flash and Wowza sides.
Meanwhile, if you want to tackle Flash rtmp multi-bitrate, you can also look at JW Player using a client-side playlist, and works, such as it is, with Wowza:
http://www.longtailvideo.com/support/jw-player/jw-flv-player-v4/27/bitrate-switching
Richard