Sorry if this is late, but I just saw this on a casting board in New Orleans:

Casting Singers and Dancers for America's Got Talent 3 - NBC
Reality TV - Non-Union
Executive Producer - Simon Cowell, James Sunderland
Casting Director: Roz Taylor Jordan
Interview Dates: None- Booked off of Tape only
Shoot/Start Date: March 29 or April 9
Pay Rate: Million Dollars to Winner
Location: LA or NYC
Submission Deadline: March 24, 2008

Sumit Auditions Tapes of Your Talent - DVD, Mini DV, VHS - to:

AMERICA'S GOT TALENT 3
4000 W. ALAMEDA AVE.
3RD FLOOR
BURBANK, CA 91505
ATT: ROZ T. JORDAN

If you are in LA, you may drop the tape off in person.

Thease should be performance tapes with groups of three or more.

TALENT GROUPS - America's Got Talent is looking for the next great
girl/guy singing or dance group to compete on our current season. We
want sizzling acts with great vocals and or choreography. Do people
compare you to Destiney's Child or NSYNC? Do you have great style,
tremendous stage presence and LOVE to perform? Do you think you are
one step away from making it? Let us give you the exposure to 12
million viewers and the chance to win one million dollars! No
audition is required and all selected participants will be booked
directly for the show. We are looking for amateurs and unsigned
artist...PLEASE ONLY SUBMIT GROUPS OF 3 OR MORE NOT INDIVIDUALS.

Sounds like they are really needing groups to submit to round out the talent.