can any one guide me to a AAC decoder for windows media player?

http://www.envivio.com/products/etv/download.jsp

a plugin/filter for WMP 6.4 or newer, RealPlayer 7.x or newer or QuickTime 4.x or newer (download size ~2.3 MB) enabling them to play all MPEG-4 multimedia content, i.e. video, audio etc. (see examples on the Envivio site).

thanx.

i would just like to know if this plugin will open audio files saved as .aac

Probably not, because it is meant as a MP4 plugin for these players that cannot play MPEG-4 content by themselves. But you can of course convert existing *.aac files to *.mp4 files with "Ivan & Menno" and mp4creator, so that they should be playable with EnvivioTV afterwards.