Your best bet is to get that usb joystick. If you for some reason went with a game port adapter card to install in that new gateway , you will most likely hate the hassle it will probably give you just to install it.
The simple USB joysticks will not even need software to get going, Just plug it in and the computer will recognize it instantly. Pull it back out and no Problems.
The better ones will need to have software installed which might take a minute or two but then it's smooth sailing.
Also USB ports are usually found in the front of the tower so no digging behind the computer to disconnect for whatever reason.