For the standard one, you will need a U-HID or some other board that has analogue input to read the pots.
For the gameport one, you'll need a soundcard with a gameport or a gameport to USB adapter.
I just ordered a "SuperJoyBox7" from fleabay (that sounds so dirty

).
(still waiting for it to arrive from china) Gameports are limited to 4 axis and 4 buttons, effectively two, two button flightsticks.
From what I gathered searching the net, this usb adapter works fine as long as you only have a 2 button joystick and they will definitely not
work with any force feedback sticks.
Don't worry too much about the pot values as long as they are under 100k, the calibration in windows should adjust for them.
This wikipedia article about gameports was very helpful to me:
http://en.wikipedia.org/wiki/GameportI also ordered a splitter that would allow two sticks to connect to one gameport (waiting for that from the uk).
I have no idea whether it will work with the usb adapter or not, but I am going to find out.
I should have some actual experience to report next week, instead of just regurgitating what I've found in researching.
After reading the wikipedia entry and learning what the pinout is, I also thought this might be the easiest way to add a pair of "joystick" guns.
Basically all you need is something to read the pots & allow for two buttons per player and this is exactly what the gameport is designed to do.
For around $12 total for the usb adapter and splitter, it would be a cheap interface.
If I get that working, I'll post a write up on exactly how to wire everything.