You cannot upload the Lytebox files directly with the template editor so you have 2 options:
1) Upload the lytebox.css and lytebox.js to your template directory with FTP and then add the following to startpage.pstpl right after the {TEMPLATEJS} placeholder:
<script type="text/javascript" src="{TEMPLATEURL}lytebox.js"></script>
<link href="{TEMPLATEURL}lytebox.css" media="all" type="text/css" rel="stylesheet" />
2) In the template editor, add the contents of lytebox.css to the end of your template.css file and add the contents of lytebox.js to the beginning of your template.js file.