RewriteEngine on
RewriteRule ^/overview/$ /cgi-bin/board.cgi?action=overview
RewriteRule ^/board/(.*)/(.*)$ /cgi-bin/board.cgi?action=viewboard;boardid=$1;$2
RewriteRule ^/thread/(.*)/(.*)$ /cgi-bin/board.cgi?action=viewThread;threadid=$1;$2