Hello
No it doesn't screw up your modemline since you can start and stop it as you wish.
In detail:
If you run Tomcat as a standalone you don't have to install anything. Just unzip the
directory structure to your harddisk, configure it and change the bat-files if
nessecary. Then start Tomcat with the bat-file and shut it down with it.
As long as you don't run startup.bat Tomcat isn't running.
One more thing it is dependend on the jdk1.2 or higher so you need to install that
first. My recommendation download jdk1.3 and use it since it has the better
performance.
Stefan