I found this on the GSM Hosting forum, post #3496786 (type it in google since i'm not allowed to post links) and did it last night. Worked on the first attempt and didn't had any problems ever since
Go to your Options : Security >> Security Options (the same page where you can enable/disable passwords) & scroll to the bottom. If there's an IT policy attached, it will be mentioned there. Remove the IT policy using these instructions
Step 1 : Ensure the Blackberry Desktop Manager is installed using Blackberry Internet Service, and not Blackberry Enterprise Server. If you are unsure, it would probably be a good idea to uninstall the Desktop Manager and start again. If you don't have the CD that came with your Blackberry, the Software can be downloaded here.
Step 2 : Download the file police.bin and save it in your Blackberry installation directory (C:\Program Files\Research In Motion\BlackBerry).
Step 3 : Wipe your Blackberry, creating a backup if necessary. Select Options/Security/Wipe on the Device. If this option is unavailable, you may have to install the latest software on your Blackberry. You need to Download and install the latest OS for your device. Connect your device, open the Desktop Manager, select Application Loader, and follow the prompts.
Step 4 : Close the Desktop Manager if it is open.
Step 5 : From the Windows XP Start Menu select Run..., and at the prompt type regedit. In the tree on the left hand side, navigate to:
HKEY_Current_Users\Software\Research In Motion\BlackBerry\PolicyManager
Right-Click the Policy Manager Folder and select New/String Value. Name the value Path. Now, Double-Click the Path Subkey and set Value Data to:
C:\Program Files\Research In Motion\BlackBerry\policy.bin
Step 6 : Open the Desktop Manager.
Step 7 : Connect the Device. Verification Once complete, the Options/Security screen on your Blackberry should not contain references to an IT Policy, you should now be able to change all settings (including password prompts), and install Third Party Applications.