You should save the oauth access key/secret you get for the account you
want to post to (if it's your application's account, you can get the
access keys from the application's page on
dev.twitter.com). You can
then use your client key/secret and user access key/secret to make calls
to the API on that user's behalf without them logging into an actual
session of your application.
This page is a good overview of OAuth:
http://dev.twitter.com/pages/auth
--
Thomas Mango
tsm...@gmail.com