Was just reviewing the standings this morning and noticed these guys at the bottom of the Points classification:

96 Alexander Efimkin (Rus) Barloworld -3
97 Juan Miguel Mercado Martin (Spa) Agritubel -5
98 Kurt-Asle Arvesen (Nor) Team CSC -5
99 Iker Camano Ortuzar (Spa) Saunier Duval - Prodir -5
100 Stéphane Augé (Fra) Cofidis - Le Crédit par Téléphone -15

http://www.cyclingnews.com/road/2007/tour07/?id=results/tour078

So... how does one achieve _negative_ points?

You get punished for some infraction by race officials. If you don't have any points, or enough points to cover the punishment, it goes negative.