There are two ways of downloading YUI4JSF library;
<repositories>
...
<repository>
<id>yui4jsf repo</id>
<name>YUI4JSF Repository for Maven</name>
<url>http://yui4jsf.sourceforge.net/maven/core/</url>
<layout>default</layout>
</repository>
...
</repositories>
<dependency>
<groupId>net.sf.yui4jsf</groupId>
<artifactId>yui4jsf</artifactId>
<version>0.6</version>
<scope>compile</scope>
</dependency>