take a look at the size of the file. if the WAV file is lower than 800 kb maybe you should put WAV file too .. 800 kb is quite big already for 56kers ... but its ok if its under 1 mb
flash streaming is good option. maybe you can put some reminder in your site to tell the user to download the flash player plug-in (flash player plug-in just take a minute to download).
thats all i could think. maybe others had any other idea ?