If you're using Firefox v2 then I know the browser has a bug that throws up 'Connection Refused' and 'Connection Reset' messages at random under certain circumstances, this is not related to ISPr though. Otherwise it works fine but you can always try a full link of /speed/index.shtml instead of /speed and tell me if that works.
However if you can reach the page itself then I know it has some problems with older versions of Opera too but so long as you have the latest version of FLASH and Opera installed then it shouldn't be a problem.