Hi,
No really what you want, but I have one site that "graduated" from modem dial-up to ADSL. Under their modem system, they used an electronic timer which basically powers off the modem when they leave work at night and turns it back on in the morning. There is even an override switch on the timer to manually turn on and off the unit as well. When they moved to ADSL (since they are not using SME for mails, etc.) they continued to use this method to disconnect from the net overnight. Crude, but very effective ! Not suitable if the adsl modem (power source) is not within easy reach though, if you intend to manually override and turn it on and off.
Kelvin