For anyone having problems with Express Scribe version 5.0 in Windows 7 regarding audio codecs, simply go to the following web site address and download the TrueSpeech Codec installer. I downloaded it to my desktop and simply opened a sound file in wav format in Express Scribe and it works!
http://www.bytescribe.com/index.php?id=32
My initial problem was only that I bought a new Gateway computer with Windows 7 and Express Scribe would not play simple wav files. I searched high and low for a solution regarding codecs and finally found it on the Bytescribe web site of all places. Prior to this I attempted to convert files as well amongst other things and nothing seemed to work. I'll be glad to go into further detail if anyone needs assistance.
I love my new computer and Windows 7 is okay so far as well.