You guys should also clear up what these options are.
They are commands that you can add at the end of a shortcut.
Create a shortcut by right clicking on srb2's folder. It'll prompt for a file. Select srb2win.exe.
In the little prompt box you should see the path to srb2win.exe. After the path, type in -win and the other commands people have suggested and finish the shortcut creation wizard. You should have a shortcut the executes srb2 with the parameter -win, which will start srb2 in windowed mode.
You should learn quickly the difference between an ingame option and a command like that, because usually people don't delve into the topic deep enough.