question on Self-Decrypting Messages !!!

 If I encrypt a message and send it to someone who doesn't use PGP, I have
 to use SDA, and somehow give them the password to it, right ?

 Is this secured and protected the same way  as Digitally signed and
 encrypted messages that someone who has PGP would receive ?

 I am a newbie in this thing, any help and explanation will be appreciated.
 Also, what's the best way to encrypt mails if I am using 'hotmail' or
 'yahoo' ?

 Thanks  a lot.