With a Windows Mobile 5 device, once it was paired with your Tablet you could create a dial up connection on your computer that would connect to the Internet via whatever data protocol your device uses (e.g. EVDO, GPRS or HSDPA).
With Windows Mobile 6 you can still connect to the Internet using your SmartPhone as a modem, but the process is slightly different and requires you to complete steps on both the device and on your tablet. The following steps outline the process. This assumes you have already paired your phone with the tablet.
1) On the Windows Mobile 6 device select Internet Connection Sharing
2) Next click the Connect button. This establishes the connection to the Internet and readies the device to accept a connection from your tablet.
Now that the mobile device is ready to accept the connection you need to go to the tablet to establish the connection.
3) On the tablet right click the Bluetooth icon in the system tray and select join a personal area network.
4) In the Bluetooth Personal Area Network Devices dialog select your phone in the Access Points area and then click connect.
Viola - you are online!