Video Resolution/Taskbar

My application requires a video resolution of 800x600. Some of my users normally run in 640x480 mode so I modified my application to change the video mode on the fly using the ChangeDisplaySettings api. When running under Windows 95 everything works fine. But when my application is run under Windows 98 the video resolution still changes but the taskbar "floats" about 2" above the bottom of the screen. I found an article that said to use the SendMessage api with HWND_BROADCAST as the window handle to resize all open windows. That fixed the taskbar problem but now I have a new problem: the Screen.Height and Screen.Width values are 0, which prevents all of my forms from being centered. Help!