Hello timeman!
We have several threads on Broadway to help you, most notably the one entitled "Playbill Collectors" in the Autograph Collecting section.
To send to a Broadway show, you send like you normally would, except address it to the:
Stage Manager of 'Equus'
c/o Broadhurst Theatre
ghfhgjfg
New York, NY 10036
(I've been there 4 times but still can't remember the address
!)
It's usually good to write about how much you enjoyed the show/actors/etc., and then request a signed playbill from the stage manager.
All playbills are roughly 5.5 x 8.5ish, and one fits perfectly in a 6x9 envelope. Two or one stamps should be fine.
To be honest, I'm not sure if EQUUS is doing signed playbills; I sent back in Sept. and got nothing, but I legitamately just sent again on Monday, so we'll see how it works out.
Good luck! Any other questions, check out the other thread I mentioned above or PM me
! Greg