I had my Megane serviced last week. 23-11-07
The dealer pressed the trip switch until the message "Service due in" came up. He then pressed and held in the small black button on the Dash (The one that resets how far you have travelled) until the Service message flashed, then he pressed it again and it re-set the service clock to 18000 miles. For the privilege, he charged me £40.00 for this. Hope this helps.
Jamie
November 2007