You generaly cannot get a license to own machineguns. You can buy a machinegun and make an application to BATFE to have it transfered to you and,pay a $200 tax. This requires that you first purchase the machinegun, then fill out a Form 4, finger print cards, submitting a passport photo and obtaining a sign-off from the Chief Law Enforcement Officer in your county. After you've bought the gun, submitted the paperwork and $200 to BATFE, you will wait 3-4 months for them to complete a background investigation on you. If you pass, the Form 4 with a tax stamp will be sent back to you and ONLY THEN, can you take delivery of your machinegun.
FYI, like others have mentioned - machineguns are expensive. AK's go for about $14,000 +/-. The lowest priced full-auto guns are usually M10's (Mac 10's), which sell for somewhere in the neighborhood of $3,500. Then you have the ransfer fee that you will likely have to pay to an NFA dealer.
Most average Joe's, like myself, bought machineguns when they were in the high hundreds, low thousands. They were still expensive, but $14,000 is out of my ballpark just to shoot a full-auto. However, as an investment, they've proven to be pretty good.