I used this specific post as my guide:
http://forums.fibble.org/viewtopic.php?p=14#2
The first step is to configure the device, and in that setup, you leave the ID and PW blank, when you configure the connection for your laptop (via Network Connections) you will enter wap.voicestream.com in the Phone Number field, and guest/guest for TMobile.
Sounds like you are getting close. Good Luck!