Lately I have noticed that the task manager in Windows XP mysteriously started hiding all the tabs (Applications, Processes, etc.) and the borders around it. I knew the shortcuts to step through all the tabs (CTRL+TAB and CTRL+SHIFT+TAB, forwards and backwards respectively) so it wasn’t a big deal but today just out of curiosity I did a quick search on google.
After my little adventure I found out that the task manager was running in a "tiny footprint" mode! Here is the first search result where I found out what it was and this MSDN article points out another way you can get out of the tiny footprint mode. You can easily switch between the two modes by double clicking on the borders of the task manager window.