This concept is really simple. Just open the window set your shutter speed high and click! Better if you set your camera to shutter priority...just make sure you have enough light so even if your camera sets your aperture really wide it's still not underexposed.
Setting your focus mode to ai servo or ai focus may help...it all depends on what you are shooting.
Here's a shot I took on our way home from Moline Illinois:
Shutter speed is at 1/800 sec, f4.5 at iso100.
I shot this while the window is closed...I was lucky it was clean!