2 related problems:

When I first installed last.fm, I was asked if I wanted to store a password in my wallet and I said no. Now, I have changed my mind. How can I store my password?

Even when I type in the username and password into the last.fm settings, nothing ever gets submitted and it doesn't seem like it is registering that I even gave it any account info. "Submit Tracks" is checked.

Any ideas what is going on and what I can do to fix it? Do I need to provide anything?

thanks!

If you selected not to use kwallet, your password is stored as clean text instead of being stored in an ancrypted way in the wallet.
Check the $HOME/.kde/share/config/amarokrc file, there should be a section for [Service_last.fm], change that.

Also please do not forget to state which exact Amarok version you are talking about, there were quite some changes between the 2.1.x and 2.2, 2.2.1 and 2.2.2 beta versions.