You can't directly connect it; you would need some board to convert the digital signals into analog if you want to use them as generic analog joysticks.
If you know how to convert digital to analog, here's the output values that need to be converted into an analog voltage. Notice the williams 49-way is binary complement of the midway/happs 49-way.
Sinistar/ Midway/
Williams 49-way Happs 49-way
1000 full up/right 0111
1100 2/3 up/right 0011
1110 1/3 up/right 0001
0111 center 1000
0011 1/3 down/left 1100
0001 2/3 down/left 1110
0000 full down/left 1111
I guess you could convert it to a binary signal compatable with the digital "analog" joysticks like the sidewinders and all USB joystick, instead of the analog discribed on the page ref'ed.