I was able to write and test my servlets just fine using Eclipse Indigo and Tomcat, then I loaded Eclipse Juno with ADT (Android Development Tools) and suddenly it won't run Tomcat. I cannot even see anyplace where I can tell Eclipse that I need to use a server.
I have tried re-downloading Tomcat (7.0.39 the latest version )but that doesn't work as it doesn't send me an executable that I can run and install.
If you downloaded and installed a Juno spin setup for Android, most likely it doesn't have the J2EE plugins. J2EE support - and for that matter, even basic Java support - isn't build into Eclipse. It's done via plugins, and the various Eclipse spins have different plugin sets.
You should probably download and install Juno for J2EE and then install the Android plugins into it. I'm not sure how much work it would be to upgrade a copy of the Android spin for J2EE support, but I suspect it's considerable.
An IDE is no substitute for an Intelligent Developer.