I've had the same problem with my new Dell XPS 3800 with 24 inch Dell monitor. I was on these forums trying to find a solution, but nothing mentioned worked. However, good news people... I found how to fix this. And it is really so simple.
Step 1 : Minimize your open windows.
Step 2 : Right click on the task back and verify that the "Lock the taskbar" option isn't checked. If it is, uncheck it.
Step 3 : Move the taskback to the top of the screen.
Step 4 : Maximize a window, any window. Now, the window will take all the space it has. It will not leave a space on top near the taskbar's new position, nor will it create a space at the bottom of the screen.
Step 5 : Keep the window maximized and move the traskbar back at the bottom the way you like it. You can lock it back into this position with the "Lock the taskbar" option as described in step 1.
Result : All windows will now take all the screen and leave no annoying space.
Let me know if it worked for you guys.