Try this, it is from the latest isue of PC Magazine:
Q
In Windows XP Professional, my Task Manager has lost the top of the program window. The Applications, Processes, Performance, and Networking tabs are gone, as is the menu. All I can see is the subwindow for the applications. To close the task manager, I must click on it and press Alt-F4. What is wrong, and how can I fix it?
A
You are seeing Task Manager's tiny-footprint mode. Available in Microsoft Windows NT 4.0, 2000, and XP, thismode is invoked by double-clicking in the border around the tabs, and it's quite easy to trigger accidentally. The window can be especially odd-looking if the Performance tab is the only one visible, as the figure shows. To bring back the full Task Manager display, simply double-click in the border again. Now that you know how to turn it on and off, you may find occasions where tiny-footprint mode is useful.