What do you mean by adding "podcast page as portlet"? the podcast itself is an xml file, rendering it passes xml mime-type, etc. That can't be embedded. The usual approach is to provide a link for the podcast. What we have done for the openacs-conference
http://oacs-dotlrn-conf2007.wu-wien.ac.at/conf2007/ was to add a podcast icon with a link, as in:
[[image:podcast.jpg|Download Conference Presentationa as as Podcast|-href itpc://oacs-dotlrn-conf2007.wu-wien.ac.at/conf2007/podcast]]
For providing a link to a single podcast content file, use
[[file:ACSkonferenz_neumann_xowiki_cutVGA.mp4|Presentation Neumann]]