Well i tried with pidgin and it works fine, make sure you can access to port 5222 other wise you can't achieve this, the procedure is simple
choose a user from zimbra
make sure to use the correct password for the user
in pidgin i tried to use my full domain name mail.something.com, but i notice that my user name wich is
user@something.com has become
user@mail.something.com so i had change to something.com and works fine so check that out and i sure gonna work

make sure that you have contacts added on zimbra webmail
