I can confirm that for the time being the border crossing at O Sm'aich/Chong Jom is open to foreigners having crossed there on the 20th of June 2005. The border is open till 8pm in the evening and, contrary to what the Lonely Planet claims, it is open everyday, not just weekends and Mondays. Pick-up trucks do 'run' to the border but they will try to charge well over the local rate which should be around 7 dollars U.S. You can either go directly from Siem Reap, Cambodia to O Smaich crossing into Surin Province Thailand or you can detour to Anlong Veng to visit Pol Pot's grave and one or two Khmer Rouge soldiers as there is a Guest House in this town but the road, as with most roads in Cambodia, is a pot-holed dirt track traversing wooden bridges/planks which plies a more or less straight route up into the poverty stricken North West of the country. Worth seeing are some of the 'jungle' temples including Preah Vihear, a Khmer temple of disputed ownership which lies on a cliff 'hanging' into the Cambodia side of the Thai/Cambodian border.
Moriarty