If you can find the file browser go to the folder /etc and look for a file called redhat-version or redhat-release. I don't know for sure if it has this, but there's something similar that is a text file saying the version in both distributions (versions of linux) I use. There's a decent chance you'll have an older version, since the current is either the Enterprise Version, or is called Fedora. This means to get all things working it may be necessary to install a new version, but you should be able to do a lot even if you still have the older version of Red Hat.
You may already have something that can work like aim on the computer. If you have either kopete or gaim, both of these can connect with aim, as well as a few other IM services. If you have one let us know and we can help configure it. Otherwise the link pixellany gave should work for you.
There's a lot of good online guides for learning about linux. Two good ones I've found are Getting Started with Linux
and Linux Knowledge Base and Tutorial
. Also a good resource to look at is The Linux documentation Project