I know your question was to Randy, but I also happened to visit Doi Inthanon this past May with a Thai friend. We rented a car - 1000 baht ($25) for the day and they held my passport - and my Thai friend drove. This is the way I would recommend - either your friend can drive or maybe will have a friend in CM who can drive and wouldn't mind a day's holiday as well. Next best thing would be to hire a car & driver, which would probably run about 2000 baht. Most hotels can arrange everything, including tours via bus, but that means you will probably be doing the tour with guests from other hotels and will be following a pre-set course. Public transportation is not a real option. We had a great time at Doi Inthanon and I definitely recommend it.