When iCal issues an alarm message (Leopard), there are 3 symbols to the right of the displayed alarm time. If you place the mouse pointer over any of the symbols, no description is provided, nor could I find any description in the help or user documentation.
From trying the symbols I have deduced that the magnifying glass displays details of the event allowing you to make changes and that the rotating arrow allows you to repeat the alarm at a later time.
I assume that the X dismisses the alarm. Is clicking the X different to clicking the red button on the top left of the message window?
Is there anything else done by these options beyond what I have described above?