Neither JBoss AS 4.2.3 nor 5.0.1 contains that class. Which JBoss AS are you using? Or do you mean another JBoss-branded product (other than JBoss AS)?
I am using JBOSS 4.X and I couldn't find either. I was doing this tutorial http://docs.jboss.org/jbossas/jboss4guide/r2/html/ch6.chapt.html#ch6.p2pjmsclient.ex and sample classes are importing import org.jboss.util.ChapterExRepository;
Apparently what you are looking at is the Guide for JBoss AS 4.0.1, but the same class is still mentioned in the Guide for 4.0.5. I even looked in the 4.2.2 Guide and that class is still mentioned.
Looks like someone asked this same question about 5 years ago: http://www.jboss.org/index.html?module=bb&op=viewtopic&t=68096.
One of the commentors offered a reply which lead me to click on the "Examples" link next to the 4.0.5 documentation on the docs home page (https://www.jboss.org/community/docs/DOC-12898), and I found the class in question in that zip file.