To remove your twitter Account from BuzzStream:
Log directly into your twitter account on Twitter.com.
Go to the Settings menu for your twitter account. Select the Applications tab.
Find BuzzStream in your list of allowed applications.
Click the Revoke Access button in the right side of the BuzzStream listing. Twitter will revoke the access.
If you decide you want re-establish the permission for BuzzStream to access your twitter account, you can restore access by clicking the same button which will now be labeled Undo Revoke Access.