Is the game port on a sound card or on the motherboard?
If it is the latter, there *will* most likely be a Game port option in the BIOS. Typically you can find it under something like "Integrated Peripherals" and maybe in there under "I/O devices". You can set a couple of DMA addresses for it or disable it. Just choose the first of the addresses if it is there....
What motherboard are you using, btw?
In Win98 you should look under "Control Panel/System", as far as I remember. In the device list that lists all the installed hardware, look under "Sound, Video & Game Controllers" or something like that. See if there is a standard game port listed and if it is working. Actually, if it is there, just remove/delete it and reboot so that Windows might detect it properly again.
Good luck!