Using Group Policy, the only thing I can see is to disable any changes to
the IE toolbars, which would include the Address Bar. So you would have to
disable the Address Bar and then apply the policy -
User Config...Admin Templates...Windows Components...Internet
Explorer...Toolbars...Disable customizing browser toolbars.
"Prevents users from determining which toolbars are displayed in Microsoft
Internet Explorer and Windows Explorer. If you enable this policy, the list
of toolbars, which users can display by clicking the View menu and then
pointing to the Toolbars command, will appear dimmed."
A better idea might be the NoAddressBar registry restriction mentioned here:
http://www.winguides.com/registry/display.php/1111/