I don't use AC but I presume it's the same method as any other app, if not my apologies. You have to use the 'alt' key together with the appropiate number for the symbol desired.
The number depends on the font, for example to get a superscript 2 in Arial, you use the key combination 'alt+0178', you have to use the numeric keypad, not the one across the top. If you want to see what symbols are available, open up character map....Mike