Mindboards

Would it be possible to either:
A- Use the NXT HID
or
B- Use bluetooth

to use the NXT as gamepad or joystick peripheral for a computer.

With all the sensors (acceleration, gyro, compass, Psp-nx) it would be really cool to make a custom controller for PC games

You can use an Arduino Uno to act as almost anything on the computer USB bus. Arduinos can be interfaced to the NXT, so you should be able to with an Arduino Uno.