You don't set thios in the index.html, but eg. the menu.html where the links are set that you want to open in, say, main.html (named "main").
There are at least two ways to do this:
way 1:
open menu.html and insert
code:
<BASE TARGET="main">
into the header if you want all links from menu.html to open in main.html (named "main").
way 2:
open menu.html and instead of
code:
<A HREF="url">Targeted Anchor</A>
write
code:
<A HREF="url" TARGET="window_name (eg. "main")">Targeted Anchor</A>
Further info:
http://www.newbie.net/frames/