Been screwing around with this for waaay to long tonight wondering why the heck it doesn't work. Either there is css styling in your style.css that is required or...
You have inline css in your demo pages, ../includes/style.css attached in the head, then there is the ../jquery.scrollbar.css which isn't referenced, but looks to contain the different 'types' all-in-one. If you remove the style.css from the demo page nothing works so there must be something in there that is 'needed'.
I've put an extremely slimmed down version of the basic.html below... what needs to be done given this example for this to work properly?
<!DOCTYPE html>
<html>
<head>
<title>jQuery Scrollbar Demo</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<link href="../jquery.scrollbar.css" rel="stylesheet" type="text/css"/>
</head>
<body>
<div style="height:150px; width:75%;">
<div class="scrollbar-inner">
<p>
Lorem ipsum dolor sit amet, consectetur adipisicing elit. Proin nibh augue, suscipit a,
scelerisque sed, lacinia in, mi. Cras vel lorem. Etiam pellentesque aliquet tellus.
Phasellus pharetra nulla ac diam. Quisque semper justo at risus. Donec venenatis, turpis vel
hendrerit interdum, dui ligula ultricies purus, sed posuere libero dui id orci. Nam congue,
pede vitae dapibus aliquet, elit magna vulputate arcu, vel tempus metus leo non est. Etiam
sit amet lectus quis est congue mollis. Phasellus congue lacus eget neque. Phasellus ornare,
ante vitae consectetuer consequat, purus sapien ultricies dolor, et mollis pede metus eget
nisi. Praesent sodales velit quis augue. Cras suscipit, urna at aliquam rhoncus, urna quam
viverra nisi, in interdum massa nibh nec erat.
</p>
<p>
Lorem ipsum dolor sit amet, consectetur adipisicing elit. Proin nibh augue, suscipit a,
scelerisque sed, lacinia in, mi. Cras vel lorem. Etiam pellentesque aliquet tellus.
Phasellus pharetra nulla ac diam. Quisque semper justo at risus. Donec venenatis, turpis vel
hendrerit interdum, dui ligula ultricies purus, sed posuere libero dui id orci. Nam congue,
pede vitae dapibus aliquet, elit magna vulputate arcu, vel tempus metus leo non est. Etiam
sit amet lectus quis est congue mollis. Phasellus congue lacus eget neque. Phasellus ornare,
ante vitae consectetuer consequat, purus sapien ultricies dolor, et mollis pede metus eget
nisi. Praesent sodales velit quis augue. Cras suscipit, urna at aliquam rhoncus, urna quam
viverra nisi, in interdum massa nibh nec erat.
</p>
<p>
Lorem ipsum dolor sit amet, consectetur adipisicing elit. Proin nibh augue, suscipit a,
scelerisque sed, lacinia in, mi. Cras vel lorem. Etiam pellentesque aliquet tellus.
Phasellus pharetra nulla ac diam. Quisque semper justo at risus. Donec venenatis, turpis vel
hendrerit interdum, dui ligula ultricies purus, sed posuere libero dui id orci. Nam congue,
pede vitae dapibus aliquet, elit magna vulputate arcu, vel tempus metus leo non est. Etiam
sit amet lectus quis est congue mollis. Phasellus congue lacus eget neque. Phasellus ornare,
ante vitae consectetuer consequat, purus sapien ultricies dolor, et mollis pede metus eget
nisi. Praesent sodales velit quis augue. Cras suscipit, urna at aliquam rhoncus, urna quam
viverra nisi, in interdum massa nibh nec erat.
</p>
</div>
</div>
<script src="../includes/jquery.js" type="text/javascript"></script>
<script src="../jquery.scrollbar.js"></script>
<script type="text/javascript">
jQuery(document).ready(function(){
jQuery('.scrollbar-inner').scrollbar();
});
</script>
</body>
</html>