Can't control fans on Asus P5B-VM (Winbond w83627dhg)

[via.lej at free.fr (Vianney Lejeune)]

Hello,

	I have an Asus P5B-VM running Debian Etch 4.0. I try to control my  
case and CPU fan using pwmconfig/fancontrol. I ran my tests with and  
without Asus Q-Fan (BIOS settings). The fan's speeds are correctly  
reported but pwmconfig is unable to control any fan. What did I miss ?

Thanks in advance,
Mr Lejeune