Proposed for the iChatAV 3.0 discussions - similar to my other FAQ
How do I reinstall iChatAV 3.x?
This is for Tiger only. To reinstall iChatAV 2.x on Panther, see this FAQ.
Download Pacifist. Insert the Tiger install DVD into the drive and open Pacifist. Click the Open Mac OS X Install Packages button on Pacifist. This will load the DVD.
Once the DVD has loaded, there is a list of the contents of the DVD. Navigate to Contents of OS Install/Contents of iChat/Applications/ directory. This is where iChat.app is located and what will need to be extracted/installed to your computer. Alternatively, you may perform a search on the directory listing with iChat.
Once the iChatAV application is found, highlight/select it and extract it to the computer by clicking Extract to or Install. Be sure to install iChatAV to the /Applications/ folder on your hard drive (not your user folder). Repair permissions after the reinstallation just to prevent any quirky behavior by using Disk Utility located in /Applications/Utilities/. Then you should be all set to use iChatAV 3.x.