I use DXWnd, and it works perfectly for Flatout 2. The place to download DXWnd from is sourceforge (as it is an open source free software) here: https://sourceforge.net/p/dxwnd/home/Home
Go to the 'Files' tab to get the download.
Once you have installed that create a shortcut on your desktop for the dxwnd.exe and use that to launch the games you want to force into windowed mode.
To do that when the DXWnd window opens (after running the exe) go to 'Edit' and select 'Add' which will ask for the game exe location, so browse for that (in this case the Flatout2.exe) in the 'Path' location (click the box with the 3 dots '...' after the 'Path:' line).
The only thing you might want to adjust is the 'Position' info under the 'Main' tab. 'Run in Window' should be checked already.
I use X=10 Y=10 W=1600 H=1024
Also i have the 'X,Y coordinates' button selected. Click 'OK' when you have checked those things.
This gives me a 1600x1024 window in my native 1900x1080 monitor.
To run Flatout2 (or any other game you have added to DXWnd) just run dxwnd,exe and double click the game launch icon in it's window, this will launch the game in the windowed mode you have set up.
This program does not always work for all games (i seem to remember i could not get Fallout3 to run with it?) but it does in this case for Flatout2.