How do I remove dried latex paint from carpet?
Depending on when this happened you might be able to just use water, or soap and water. Before it cures, latex paint is water soluble (so the absolute best time to clean it up is before it dries at all). I've had good luck using a couple of sponges and warm water - one to apply fresh clean water to the paint, and the other to blot up dissolved paint/water. You can continue this until the spot is gone.

If the paint is cured (i.e. the water isn't breaking it down) then there is a cleaner called "Oops!" that works well on paint, ink, tar etc on carpets. I would try some of that as I've heard it works wonders. It should be available at your local hardware store.