If you already use thickbox on your site, there's a simple way to integrate it with the ImageFlow script by Finn Rudolph.
Make sure you have the thickbox.js, jquery.js and thickbox.css scripts uploaded to your server, and referenced in the head of your web page.
<script type="text/javascript" src="js/jquery.js"></script>
<script type="text/javascript" src="js/thickbox.js"></script>
<link rel="stylesheet" type="text/css" href="styles/thickbox.css" media="screen" />
Change the longdesc attribute for each image to:
javascript:tb_show( 'caption', 'images/image.jpg' , 'slideshow1' )
where 'caption' is the caption of the image, 'images/image.jpg' is the URL of the image and 'slideshow1' is the imageGroup of the image.
Note: the imageGroup option can be left blank if you do not want thickbox to add the images to a group. Setting it will allowing you to click prev / next while in thickbox to scroll through your images.
Small CSS fix: Open thickbox.css, and change the z-index of #TB_window to something higher than 10002. I changed mine to 10200. The z-index of the #scrollbar and #slider in imageflow.css are 10001 and 10002 respectively. #TB_window must have a z-index higher than both of these.
There is no step 4 ;)
You can preview my hack here