I'm not quite sure I am clear on what you're trying to do.. You are trying to link from one page to the section of another page?
<a href="SEPERATEPAGE.HTML#section1">Super Epic Link</a>
where the #section must be an anchor you drop into where you want to jump to (which will be within SEPARATEPAGE.HTML somewhere):
<a name="section1" />
That is if you just want to like to the section. Unless you wanted to actually preview the actual part of the page from within INDEX.html without leaving the index page?