Santiago,
Vista no longer uses 'autoexec.bat', it will parse any entries in there to
set environment variables but that is all.
On a clean install of Vista there is a single dummy entry in this file.
This is also a system protected file, you should consider very carefully any
modifications to system protected files.
Perhaps if you could explain what you are trying to accomplish with the
autoexec.bat file someone could help you do the same thing using Vista's
normal procedures.
Michael