You dont need a lawyer, this is it right here...
To register your song with the Copyright office, do the following:
1. Send a request for a form PA application to the Copyright Office, Library of Congress, 101 Independence Avenue, S E., Washington, D.C. 20559-6000 or download the application from the website:
www.copyright.gov
Note: To order an application by telephone, call (202) 707-9100.
2. When the application is completed (properly), send it back to the Copyright Office with:
(a) If unpublished - One copy of manuscript, lead sheet OR sound recording of the best edition…or
(b) If published - Two copies of manuscript (sheet music) OR a sound recording of the best edition…and
(c) The appropriate non-refundable registration fee, which is presently $45, by money order, bank draft or check, made payable to Register of Copyrights.
Now, the wait time for application processing, and getting you your certificate back in the mail is kind of long (about 5 to 6 months), but your song is actually registered as soon as the Copyright Office gets your package (if everything is correct in the package; the application, and the fee).
Hope that helps,
dac