mucexample.html is in the CAXL SDK under doc/examples
You can also find the mucexample.html online here:
Here's the link from the library index:
Cisco doesn't have an API for that, only CAXL, which is web-based and uses BOSH (7335), not 5222.
You can use a variety of open source APIs that should work. I've played with Smack (Java), and I found it very simple to use.
If you want to see how others do it, there are at least two open source Jabber clients that use XMPP and 5222. Pidgin is one, Jitsi is another. You can download the source for each and have a look.