how can i use an expect script to do a passwordless ssh login and run a script on a bunch of remote hosts? I do not want to use public key authentication as this would require me to setup the keys on the clients etc....
Keys exist for a reason. Kludging stored passwords into a system designed to prevent you from kludging in stored passwords is a very bad idea. It's almost impossible to keep stored passwords secure.
Sometimes people have used expect temporarily to copy lots of keys to different servers.