0. Save lots of money. Plan on spending 10 times as much as a semi-auto version of whatever you want.
1. Read the NFA FAQ:
http://www-2.cs.cmu.edu/afs/cs.cmu.e...st/nfa_faq.txt
2. Move to an appropriate state as indicated above. Pick a jurisdiction where the Cheif Law Enforcement Officer (CLEO) is _known_ to willingly sign the necessary paperwork (many refuse to even when ownership is legal - no signature, no gun).
3. Find a Class III dealer in the state to buy from or transfer through. He will provide all the paperwork you need - just do everything the paperwork requires.
4. Find what you want to buy and order it.
5. Wait. Receive. Joy!