Adding code to index.htm

Hello.

I’m trying to add the slimbox picture viewer to my wordpress site but can’t seem to find the index.htm file so I can insert the .js tags.

When I View Source in Firefox I get the index.htm file – but it’s not in my root directory at all. When I look at index.php it’s only got about five lines of code.

Can anyone help me find index.htm or tell me how I add code to this another way?
Any other slimbox help for WordPress would be nice too?

Thanks.