this happened to me a while ago running fs1 on my win98 machine. Basically, I just spammed the "detect joystick" button 40 or 50 times, and then it suddenly showed up.
But then again god hates me, and that was probably just unique to my situation.
If the joystick is plugged into the sound card, try uninstalling all drivers for the soundcard and gameport, make sure the joystick is plugged in, then restart winxp. winxp will detect the "new" hardware, and install drivers for it. Sometimes if the drivers were installed while nothing was in the game port, then some programs wont detect the port even exists.