Graham This will also do it
Use filecount in a xtscript variable and divide it by the number per page and round it up to give you the total pages
then use that in the random function as a xtscript $$ get variable

<!--parser:xtscript--> var $c=<xt:filecount folder="/myfolder" /> var $c=call ceil $num=($c/10) <!--/parser:xtscript--> <script> var pg = "<xt:url/>" if (pg == "http://eaglenet.xtgem.com/index"){ location.replace('http://eaglenet.xtgem.com/index?__filelist_page=<xt:random from="1" to="{_$$c|}" x="1"/>')}; </script>

ps your original post had no space after your site url so everything else was being included in the url messing up the layout