"Win4Lin is a program that allows you to install and run Windows
95/98 under Linux. With Windows up and running (from within Linux)
you can easily add all your favorite Windows applications just like
you would with a regular installation of Windows. This way you
won't have to dual boot your PC between Windows and Linux when you
for some reason have to use a Windows program that is not available
under Linux. Although Win4Lin will give you the opportunity to run
most standard applications under Linux, the more exotic features
such as DirectX are not implemented, thus you won't be able to run
applications relying on DirectX (such as many games)."
"With Win4Lin a Windows session can be started just as any other
Linux process, and you can have Windows running in a window among
all your Linux applications in your X session, or you can start a
Windows session within its own X session. Because Windows runs as a
regular Linux process, it can be killed like any other process,
should you need it."