ssh, sftp, and public key authentication

[dave]

Hello,
    Thanks for your reply. I have done this. My problem comes in when i ssh
from offsite to the first machine, this works fine uses password
authentication. Then if i go from that box to the second machine i am
prompted for a passphrase, which i don't have for that key. Basically, three
machines are involved, machine1 to machine2 lets me in no questions,
machine3 to machine1 also works this one uses password authentication, but
then going from machine1 to machine2 does not.
thanks.
Dave.