Please read the INSTALL file.

To summarize, you need to build a bootstrap version of omake, then use
the bootstrap executable to complete the build.  Run the following
from a console window (you may need to use the Visual Studio Console Window).

   nmake -f Makefile.nt bootstrap

Next, open the .config file in a text editor and tweak the build parameters
(including the installation directory) if needed. Now, run the following 
from a console window (again, you may need to use the Visual Studio Console
Window).

   nmake -f Makefile.nt install

If you have already created the .config or if you are happy to use the default
build parameters and the default installation directory, you can skip all the
steps except for the very last one.