http://forum.doom9.org/showthread.php?threadid=84500&highlight=headac3he - one transcoder that can do it - Headac3he
http://ac3filter.sourceforge.net - a versatile AC3 decoder - though to het to wav, you'd have to go through the file writer plugin of a player such as winamp, or lay it out with Graphedit.
Another one I was thinking of, a very versatile transcoder - GX:Transcoder
It's a pretty chunky program - the other approach is with Besweet and Besweet GUI
Did you install the other plugin (multichannel wav) - that may enable the simple Nero method.
- just checked, and with only the Nero AC3 plugin in the specified directory (for my Nero 6.3), I downloaded a sample AC3 clip, - not a valid format before adding the plugin, able to add, play, and burn (to image recorder) after.
The AC3Filter gives you a lot of control - the LFE channel, you can drop or mix through, as LFE may be below the capability of standard speakers or headphones, and removing it may give extra headroom for the rest.