to install things in fedora, use yum. Since you are going into a Linux class get familiar with the CLI. Go to
www.fedorafaq.org to learn how to set up yum. From here you are download and install the java package to get the chats to run. Or hit the java site for the linux plugin. As for Yahoo messenger, you shuold be able to set up Gaim to access it. It is automatically there with a default install under internet>IM message.