Some programs and games are fussy about windowed mode, and in some programs, if you don't use their "windowed" mode option, which in most cases forces it into a much smaller window than you really want in order to use it, then sometimes it seems like you don't have much choice other than Fullscreen, or using a windowed mode that is smaller size than you want and sometimes without option to adjust the window (such as the case in RailWorks).
Anyways, good news I have for you. I have found a way.
With the use of a neat little freeware utility I found a while ago when I was trying to force some other stubborn games I have that didn't want to do Windowed mode, or didn't have the option.
The name of the utility is DXWnd.
Unfortunately, it seems perhaps the utility is discontinued and the original Developer's website of this utility may also be gone as well.
Bit, no worries, I still had the original zipped file of this. It's a self-executable little program.
I just tested it with RailWorks, and good news, success, runs in a new window like you want, and still with full access to the task-bar at bottom of screen.
I've upload the file for you on my site, you can download it here:
http://www.rryard.com/files/dxwnd.7zUn-zip it, having all of the files that come with the pack within the same folder, then run (or set a Shortcut to run) the "dxwnd.exe" file.
From the top menu of this utility, click on the "Edit" option, then select "Add".
Navigate to where you have RailWorks installed, and add the "RailWorksProc2.exe" file to the list.
Example of path; "C:\Steam\Steamapps\common\railworks\RailWorksProc2.exe".
The file will be added to the list.
Right-click on the file-name on the list, select "Modify".
Choose the following option (this is what seemed to work best for me):
Under "DirectX version to hook" choose the "DirectX 9", then click on the OK button to save the changes.
Now, when you want to run RailWorks in a nice window that nicely fills your main screen area, but leaves you with your bottom Windows-task-bar accessible, first run the DXWnd program, now, launch and run your RailWorks program as you normally would through your Steam-client, now the main RailWorks program should be running in a nice window for you.
Profit!
After closing RailWorks, you can simply close the DXWnd program as well.
Hope this works for you.
Cheers! --Don.