I checked with Microsoft and found that no updates have been released for that joystick to work with Windows XP...the most recent version is this one, which is for Windows 95/98.
The only suggestion I can make is to try using Windows XP's Compatibility Mode. To do this, find the executable, right-click it, select Properties, select the Compatibility tab, and tell it to imitate Windows 95/98. If that doesn't work you'd have to purchase a new joystick as that one is no longer supported.
The software which came with this Joy stick, which was used for MS Flight Simulator 2000, is not compatible with Windows XP. How or where can I get a driver which will enable me to use this as previously. I understand that the unit itself will work, it's just that I need the software.