Hi there,
if you have deleted iChat or other Apps that were installed when you got your Mac...there are a couple of ways to put them back on.
You can either boot from the Install CD DVD and do an "Archive & Install" this will retain your documents and settings, but will reload the Apps that you deleted.
Or you can download an Application called
Pacifist, this will allow you to 'selectively' reinstall just the Apps that you want from the OS Install disk...
So if you accidently threw away Safari you could use Pacifist to just reload that.
regards
Ric