I recently uninstalled Display Fusion and realized I lost the function of dragging a full screen window from one screen to another. I have a duo screen setup at work and that function comes in very handy. I did not realize Windows XP did not provide this function by default and only found out after I uninstalled Display Fusion. Aside from giving me that function, it also has several hot keys built-in (freeware version) and you can customize hot keys in the pro (paid) version. The built-in hotkeys include centering a window or moving a window from one screen to the next. You can also maximize a window across both of your screens.
This program also allows you to customize your wallpaper to span over two screens. You can effectively create a panoramic wallpaper for your computer if you had two side by side pictures. Better yet, use a very wide picture such as from Wikipedia. I originally downloaded Display Fusion to get two different photos be shown as my wall paper. Now I find it to be one of my favorite little utilities.
Why don't you give it a shot. Let me know if you like or dislike it. Would you like to see more of my favorite freeware recommendations?