Alt is normally the access key modifier, e.g Alt-c will trigger the link associated with the c character.
When assigning access keys you must avoid using characters that are also used by the browser with the Alt modifier. Here is a list:
Reserved Keys in IE 5.5/6 F - File E - Edit V - View A - Favorites T - Tools D - Address H - Help Reserved Keys in NS 7 F - File E - Edit V - View G - Go B - Bookmarks T - Tools H - Help W - Window Reserved Keys in Opera 7 F - File E - Edit V - View N - Navigate B - Bookmark M - Mail W - Window H - Help