You can register any lower. If it is a postban it would have to follow all the rules (by the time it is approved though, the ban should be history, hopefully).
1. You need to fill out a Form 1 (2 copies)
2. Get fingerprinted on FBI fingerprint cards (2 copies) (Blue ones they should have these at Local PD)
3. Fill out a Certification of Citizenship form (1 copy)
4. Get your Chief Law Enforcement Officer to sign your Form 1's
5. Write out a check for $200 or Money order
6. Wait 3-4 months for your application and tax stamp to come back.
7. Have your receiver engraved (M. Smith Anytown, NH)
8. Keep a copy of your Form 1 with you whenever you are using your rifle.
All of the forms can be ordered for free off of the ATF website.
This was the info given to me by a member here on AR-15 I sent mine in 6wks ago 16weeks to go!