Getting password-cache.el to work with tramp

[N.Davis]

Hi,
  I'm running emacs 22.3.1 which comes with tramp. I want to be able to 
  edit files on a number of machines without being repeatedly being 
asked for passwords, without necessarily having to use ssh keys. Tramp 
"out of the box" repeatedly asks for (forgets) passwords. It looked like 
downloading password-cache.el was a good idea to fix this, however, it 
doesn't seem to work.
  I put password-cache.el in the same directory as modes which are 
definitely picked up in the load-path.
  I added (setq password-cache-expiry nil) to .emacs.
I also tried adding
  (setq password-cache t)

I tried requring it and explicitly loading it too.

However, on starting emacs and trying to access remote files, it still 
repeatedly asks for passwords.

I have very little experience with including other .el files for emacs.

Is there something elementary/stupid I've failed to do here or does 
anyone have any pointers?

Thanks a lot,
Nick