How can I prevent accidentally quitting an application?
You can do the following to make it a little bit harder to quit Adium by accident. I think this should solve your problem.

Start by opening System Preferences > Keyboard.




Click Keyboard Shortcuts in the pillbox above.
Make sure you have Application Shortcuts selected in the left bar.
Click the + button to add a new shortcut.





Select Adium from the Application dropdown.
Type "Quit" in the menu title field.
Put your cursor in the Keyboard Shortcut field and type Command-Option-Q
Click Add




And you're done. You can close your System Preferences because the Quit command in Adium has been remapped to a less-likely-to-be-accidentally-typed shortcut.