Next time shift into neutral, that way all you have to worry about is the brake. Sounds like you don't need to much distraction so taking the clutch out of the picture sounds like a good idea.

 

Were you running the stock tires? I think that the stock so2's are the biggest factor when it comes to spinouts in inclimate weather.

 

Exact same thing happened to me! It rained previously and the roads weren't soaked... but they were wet. I didn't think it was a big deal. I was late to class so I gunned it and as I shifted from 1st to 2nd the rear broke loose and I was SO close to pulling a 180. Luckily I was able to correct it but nevertheless it scared the SHIT out of me.

Sad thing is, when I got to class my teacher was 5 minutes later than I was.

I've learned my lesson and I will NEVER speed on any wet roads again.

 

He's got a 2004, so he's probably got the Potenza RE050s not the S02s. The RE050s are supposed to handle better in the rain than the S02s, but don't forget they're still summer tires. I don't know about the RE050s, but I remember reading the S02s are rated to run at 45 degree weather and above. The rubber compound on summer tires are meant to run in warm weather and they will slip on cold pavement. In the rain, even if the temperature outside is 45 degrees, the pavement is probably colder, combined with the reduced traction from the rain is a big no-no.

If you're planning on driving your S2000 year-round, getting a 2nd set of wheels and mounting some good winter tires or all-seasons would probably be a good idea.

 

When you mis-shifted, you were literally slowing down you car by using your trainsmission. Shifting from 5th to 2nd, you induced a "shift lock", that means your transmission slowed down your S so fast that your tires didn't have enough time to do their jobs, therefore the limit of the tires' traction was exceeded and your car started to slide. You can use it to drift your car under a controlled environment(remember, no heel toe on this one, you want to jerk your car and kick the tail out. It is fun but it is not too good for the transmission though.

Oops, sorry for the encouragement here.

Personally, I don't even want to drive me S with high performance tires in the winter. Even when the road surface is clear, the low temperture alone will catch you off guard (black ice, harden rubber, sand...).

Get yourself a set of LM22(the best insurance you can buy), they will get you through Winter.