To minimize back to desktop hit Alt + Tab.

To run CFS3 in windowed mode edit the target line of your CFS3 desktop shortcut as follows:
Right-click your CFS3 desktop icon, select properties, to the target line add -window so that it reads something like this:

"C:\Program Files\Microsoft Games\Combat Flight Simulator 3\cfs3.exe" -window

To set the resolution in window mode add another -1024 for instance, note only the next smaller cxompared to your desktop resolution will do.

"C:\Program Files\Microsoft Games\Combat Flight Simulator 3\cfs3.exe" -window -1024

While we are at it other usefull parameters:

-time
enables time compression.
Keys right out of my head are CTRL + Shift + E to increase time,
CTRL + Shift +R to decrease time compression

-m3dview
Turns your CFS3 into a model viewer with some options to view inner workings like damage boxes and such.
works best if you make a copy of your shortcut first.

Mark, it's already answered in my above post.
If your screen resolution is, say, 1280 by 960
add -1024 to your shortcut.
The next lower resolution compared to your desktop resolution is the best you can get.