Most in-window air conditioners are meant to fit inside vertically-sliding windows only, meaning those with larger, horizontally-sliding windows in their house are left out. DIY web site Instructables shows us how to easily mount a standard A/C unit in a horizontally-sliding window.
While it isn't the prettiest solution, desperate times call for desperate measures, and if this summer heat has you at the end of your rope, you can install that air conditioner just by building a frame for it. All you need is a few 2x4s, some plywood scrap, and a few standard tools.
The guide will work for windows of all sizes; you just need to make sure you measure your space correctly so that your air conditioner fits. And, if you plan on making this set-up a bit more permanent, you could always use a large piece of Plexiglas instead of the plywood, to make it look a little nicer. Hit the link for detailed instructions, and let us know your makeshift air conditioning tips in the comments.
Mounting a Standard Air Conditioner in a Sliding Window (From the Inside, Without a Bracket) [Instructables]