I have my computer next to the window, and I live in Michigan, so I'm looking forward to the free cooling. What I plan on doing is opening the window ~2-3 inches, duct-taping/insulating half of that, and funnel the other half into the side of my computer. Cut-to-fit screens are optional.
Edit: About precipitation, I'm thinking of curling the 'air duct' into a bell-curve shape, that way if any water did find its way into the duct, it would just slide back down/out.
That's actually not a bad idea.
Although I live in south Florida so I only get about 2 months outa the year where it gets below 70 at night.
Can't wait till December >.<