Can sympathise with your issue. All the searching results in failure - been there done that....I too did have this very icon on XP that you refer to. Indeed on my wife's desk top XP set up it is still there and as we're accessing broadband via the same BT router I can log on to her machine to "read" the download speed which other posts tell us BT does'nt seem to accept is possible.....???? At time of writing this is 7.2mb/s which is pretty good I think. My ISP quotes 8mb/s so I think I'm getting a good result, but then I am only 800 yds from the exchange. I did restore the icon briefly on my set up, but when I next booted the computer it had disappeared and, no matter what I try, I can't make the process to display it work any more. It does involve making some change to the UPnP setup, but other than that I can't see how it can be achieved. When you get it right a further icon appears under the network connections panel(with the 1394 and the LAC it makes three icons ) from where you can select the option to display an icon in the task bar. Whether my antivirus upgrade software (AVG 8_full version) is responsible I can't say as I had installed it around the same time.......
Point is you are spot on....this icon is out there somewhere and you don't have to buy software; it's built into windows if only it can be found. Oh! and my ISP has been no help either and keeps referring me to a web site where I can get a speed check all very time consuming and fiddly when with this icon hovering over it gives you the speed instantly!
Not much help, but perhaps the wizkids out there will now better appreciate the issue you and I are trying to resolve.