RewriteEngine On
  RewriteRule /board/([0-9]*) /perl-bin/board.pl?action=viewboard;boardid=$1 [PT]
  RewriteRule /overview/(.*) /perl-bin/board.pl?action=overview;$1 [PT]
  RewriteRule /thread/([0-9]*)/(.*) /perl-bin/board.pl?action=viewThread;threadid=$1;$2 [PT]