If your referring to using the BlackBerry as a modem via Bluetooth. It is not possible. You can only use the BlackBerry as a modem if tethered via USB cable. There are a number of posts on how to use the BlackBerry as a tethered modem. One is even a stickied thread,
HOWTO: Use BlackBerry As Modem For Laptop!
An even shorter answer is...
- Call Cingular and add tethering to your account (extra charges apply).
- Download and install Cingular Communication Manager. Reboot when prompted
- Launch Cingular Communication Manager and follow prompts.
- Browse web using BlackBerry as modem.