[CentOS] OT: virtual host for apache/tomcat servers

I hope someone here can answer my question so I don't have to join another mailing list, on too many as it is...

I have the following installed: httpd-2.2.3-43.el5.centos.3 tomcat5-5.5.23

I have a small jsp app that I can hit through apache like:

http://www.mydomain.com/tomcat/myapp.jsp

So tomcat in the url above is the apache proxy address for the tomcat server.

I want to setup a virtual host in apache to automatically load this app if I type:

http://myapp.mydomain.com

I'm having trouble figuring this out. If I try to setup a virtual host, apache complains that /tomcat is not a valid DocumentRoot. Looking at tons of docs, but not seeing the solution.

Any help is appreciated.

Thanks, James