<p>In an application that I am currently working on, a requirement is to bring a window of an external application to the foreground.  Making Win32 API calls such as BringWindowToTop and SetForeground window do not work all the time.  This is due to some restrictions within Windows XP.  What I would like to do instead is send simulate a mouse click the window's button on the taskbar which I am hoping will bring the window to the front.  Does anyone know how this is possible?</p>

It's possible. But it's extremely sketchy. Your application may also break with the next version of Windows, since it's undocumented. What you need to do is find the window handle of the taskbar, then find the window handle of the child window representing the button, then send it a WM_MOUSEDOWN (I think) message.
Here's a bit on finding the window handle of the taskbar:
http://www.codeproject.com/
FWIW, the restrictions on BringWindowToTop/SetForeground are there because it's irritating when a window steals focus. That may not matter if you're working on a corporate environment. Just keep it in mind. :)