Tomcat Virtual Directory

You can create an individual context.xml file, to define a context.
You then specify the base directory for that webapp, whereever it is.

In Tomcat4, this file goes in the appBase directory (default = $CATALINA_HOME/webapps
In Tomcat5, this file goes in the $CATALINA_HOME/conf/[enginename]/[hostname]/ directory

(Context path="/my_site" docBase="C:/my_site")

(/Context)

Other usefull article: http://gandhim.wordpress.com/2008/01/31/tomcat-55-virtual-directory/