Recently John Resig posted on his blog the oldest version of jQuery he could find. So it's not really the original but he did find a version from a couple of weeks from its release (2006).
The code is annotated by John with his comments which are my favorite part.
Make sure to check it out, it's a really good read.
Did you know jQuery was almost called JSelect? Let's be thankful jselect.com was not available!