The idea of calling "vsvars32.bat" is that it sets environment variables used by the C compiler to find header files, libraries, etc. So it has to be called in the same environment as EiffelStudio.
One way to do it is as follows:

1. Open console window (as an alternative, run "cmd" from Far).
2. Run "C:\Program Files (x86)\Microsoft VisualStudio 10.0\Common7\Tools\vsvars32.bat"
3. Run "C:\Program Files(x86)\Eiffel Software\EiffelStudio 6.2 GPL\studio\spec\windows\bin\estudio.exe"

Does it help?