thinkpad t400 libreboot flashing beaglebone black how to wire atx powersupply?

> The 3.3v pin on the
> soic 16 clip goes to th atx
> powersupply's 3.3v pin?

Yes the 3.3V pin on your clip goes to the 3.3V DC supply

> Do you have to wire 3.3v pin
> and a gnd pin on atx
> powersupply to pins on the
> beaglebone black?

According to the page you provided, it is good practice to wire the ground pin on the power supply to ground
on the beaglebone (bbb). Ground on the bbb are pin 1 and 2

You don't need to wire 3.3V to the bbb, only to the chip