Just an FYI, I'm still waiting on stamps.com to send me the information for the API. It's weird, they have a great looking front page for developers but once you fill out their (very long) registration form, you are sent to a page that mentions only a PDK development kit with Active-X, Visual Basic and C++.
I'll post back if I get anywhere. In the meantime, I am working to try and move my client over to the USPS site instead. I will then still have to learn that process.