I've got a Honda 90 and have been winterizing it here in Minnesota since
1998 and it's still alive. A great engine, I might add.

Charge up the batteries. Put fuel stabilizer in the gas and mix it up.
Put the muffs and water hose on it, turn on the water and run the motor
till it's good and warm. (Make sure water is running out the "pee" hole
while this is happening.) Drain the oil from the engine by removing the
cover plate and the plug on the starboard side. Drain the oil from the
lower unit by removing the plugs on the top and bottom (Inspect the oil;
if it's milky, see your dealer). Replace the oil filter (kind of a messy
job; put a bunch of paper towels below it and handle with a Ziplock
bag). Refill the engine oil with a good grade of 10-30W. Replace the
lower unit grease with the GL-5 80-90W gear oil from the bottom plug
till it comes out the top plug. Put in the top plug, then the bottom.
Take off the prop, lube the shaft with light oil and put it back on. Put
the muffs back on and turn on the water again. Start engine and run
enough to distribute the new oil through engine. Check engine oil level
and adjust as needed. (This is the last adjustment I have ever made to
the oil level in this engine.) Idle it down and squirt fogger into air
intake till engine stalls. Turn off water, take off the muffs and spin
engine over just enough to get water out of water pump. (Some people now
pull the plugs and squirt fogger into individual cylinders, but I don't)
Make sure the motor is in a vertical position so all the water drains
out. Put 600 milliamp trickle charger/maintainer on batteries, plug in
and you're done. (Some people take out the batteries and take them to
bed with them to keep them warm all winter, but I don't. It only gets
down to -35 here.) Email me with questions.

If you are lazy, the only thing that is absolutely essential in a
freezing climate is that you make sure the motor is in a vertical
position so all the water drains out of the cooling system. Otherwise
you can buy a new engine in the spring.