You can download driver for iRiver iFP-500T 1.11(UMS-US) here, but DriversKit`s Team strongly recommend you to use Driver Updater Pro for finding the latest version of this driver. You can download Driver Updater Pro here.
Also you can:
Search iRiver iFP-500T 1.11(UMS-US) driver at Google
Search iRiver iFP-500T 1.11(UMS-US) driver at Yahoo