Just testing addition of Amazon's Widget Source MP3 widget example playlist to see if it works here. Widget Source uses swfobject.js instead of <object> and <embed> tags to display the flash file. The code is cleaner and it does not cause validation to fail. The example below is a mini version of the MP3 widget, which shows album covers at the usual size.
Switch to the HTML editor to paste the script, and don't switch back to the Visual editor after you do so. I use the RawHTML plugin for a little extra insurance against inadvertent code rewriting by WordPress. If you have it, just paste the script inside "raw" comment tags. The syntax is <!--start_raw--><!--end_raw-->.
Remember to enclose the lines of script inside the <script> tag in CDATA tags for XML compatibility and comment them out so that they do not break the javascript:
/* <![CDATA[ */
[lines of code]
/* ]]> */
