We prefer to use the simple name "Tomcat" instead of "Apache Tomcat". That's because otherwise people get confusion between the "real" Apache (httpd) server and Tomcat itself, since they're both Apache products, but Apache httpd is the more popular of the two programs. Also because it's very common to connect Tomcat to Apache, and it helps up figure out which is which.
Only one application server can own a tcp/ip port on a given computer. So if you already have a joomla server running, you have 2 choices:
1. Shut down joomla
2. pick a different port.
If Joomla were a J2EE webapp, you could also configure it to be a second webapp within Tomcat, but if I remember correctly, Joomla's not written in Java.
Really evil people (like me) can also do creative things with proxy servers and stuff like that, but that's a bit much to start with.
An IDE is no substitute for an Intelligent Developer.