I was told to bring this here in hopes someone might be able to point me in the right direction.

What are the BATF laws on turning a rifle receiver into a pistol?

If I were to take a rifle, chop off the barrel so it is 3-4", remove the shoulder stock and made it so a stock cannot be installed, and modify the receiver, is this still a "short barrel rifle" in the BATF's eyes? Technically it is a pistol. What are the regs on a non class 2 average Joe doing something like this? Do I have to get it registered with BATF, or is it ok because it is a personal built receiver for my use? Do I have to engrave serial #'s on it? How does this work?

What if it was a preban receiver?

You cannot make a pistol from a rifle receiver (meaning it's had a shoulder stock attached).  If the receiver was originally assembled into a rifle, it can only be made into a short-barreled rifle.

Strangely enough, you can take a pistol, add a long barrel and a shoulder stock (making it a rifle, temporarily) and later reverse the procedure and go back to a pistol.  I guess the logic goes that, having been a pistol, you're not making a pistol from a rifle receiver in that case, but restoring a pistol to its original configuration.

If you want to build a pistol on an AR-15 receiver, you have to start with a 'virgin' receiver, and then are constrained to build it into a post-ban legal semi-auto pistol.  Basically, this can't be done with standard parts, due to the 50oz post-ban 'assault weapon' weight limitation.  

Read up on some of the previous posts in this forum regarding AR-15 pistols, and you'll get the full story there.