right click on a toolbar (in i.e) and make sure there is a tick next to adress bar, if not, click it.
also try moving other toolbars around,
The address bar may be shoved to one side. You may need to uncheck 'Lock Toolbars' (View -> ToolBars -> Lock Toolbars) in order to drag any Toolbars at the top of the Window.
If that doesn't work go to Run on the Start menu and type 'regsvr32 /i browseui.dll' (without the quotes) this should reset the toolbars to their default state.
If all else fails go to Add/Remove Programs in Control Panel, select Microsoft Internet Explorer and try the Repair option.
hope this helps,
Mike