I have a thesis template with external chapters, preamble, etc. when I compile the main file I have error of si.sty file is not found. I really don't understand where is it? What shell I do? If I am not wrong I understand that si.sty is a package file I might don't have. If so where can I get it and wehre to put it?

Please help me. I am beginner of LaTex. I use WindowsXP and TexMaker

Thanks in advance