OSX - Get iChat to automatically log back in

Put a small apple script into your crontab which will look in the System Events log and tell iChat to login if it sees the disconnect event in there.

In a terminal:

crontab -e

*/5 * * * * osascript -e 'tell application "System Events" to if (processes whose name is "iChat") exists then tell application "iChat" to log in'