Barton,
Though I haven't worked with NT4 in a while, now, I can tell you what works for me:
Server: smtp.gmail.com
Username: Fully-qualified email address
Password: Obviously the password that goes with the Gmail account
I like to use TLS, but you can also use SSL.  For Gmail, SSL uses port 465, TLS uses port 587 (
http://support.google.com/mail/bin/answer.py?hl=en&answer=78799).  You can also use port 25 without SSL or TLS, but Gmail limits you to sending email only to other Gmail accounts, and not to any other address.  So to be useful, anymore, you need to use SSL or TLS
To use TLS/SSL with NetTalk (retrieved from 
http://www.capesoft.com/docs/NetTalk6/NetTalk3.htm#NetEmailSend_Example_Code):
  ThisEmailSend.SSL = 0 ! Set to 1 to use SSL
  ThisEmailSend.SecureEmailStartTLS = 0 ! Set to 1 to use StartTLS
  if ThisEmailSend.SSL or ThisEmailSend.SecureEmailStartTLS
    ThisEmailSend.SSLCertificateOptions.CertificateFile = ''
    ThisEmailSend.SSLCertificateOptions.PrivateKeyFile = ''
    ThisEmailSend.SSLCertificateOptions.DontVerifyRemoteCertificateWithCARoot = 0
    ThisEmailSend.SSLCertificateOptions.DontVerifyRemoteCertificateCommonName = 0
    ThisEmailSend.SSLCertificateOptions.CARootFile = '.\ca_root.pem'
  end
  if ThisEmailSend.SecureEmailStartTLS
    ThisEmailSend.SSLCertificateOptions.DontVerifyRemoteCertificateCommonName = 1
    ! Fudge this for now, as the certificate is not known
    ! when NetSimple does the CommonName check
  endIf you don't have a 
caroot.pem file, snag one from the examples.
Does this help?
Regards,
Flint