How to automate web login and file transfer

I work for a software company and I need to send medicare/medicaid.. claim files through several different secure web sites. I need a program that will connect and transfer / retrieve a file with no user interaction, preferably with the ability to pass it the login and password which could change. Does anyone have any experience using a program capable of doing this. It must handle multiple cookies. I’ve tried httpanalyzer but didn’t get too far with it.