query about tex mode functions

Greetings,

A naive query about tex mode from a new user of xemacs (on Windows XP):

When I  run the command tex-buffer I get an error:

"searching for program:  no such file or directory, /bin/sh".

Of course /bin/sh is probably the wrong place to look for something or 
other - but how do I provide the right place?

I also noted that a variable called tex-zap-file is supposed to be set to 
the file name, but it is always set to nil, and for some reason I can't set 
it using "set variable".

I have miktex installed on my machine, and it works.

Can anyone tell me what I am doing wrong?

thanks,
Michael