I assume to try to measure the power consumption of your PCI board.
I think this is a tough one. Not very trivial at all (unless someone knows of a easy way)
Most Amp Metters use a series resistor that is accurate but very low in value that it won't interfere with the circuit it tries to measure.
You probably have to do something similar but in such a way not to interfere with the power supply to the pci board which is not easy.
I would try to put a precision resistor before the power regulator of your board but this may only give you a ball part figure since the power regulator is not 100% efficient.
A more accurate but intrusive method is to put a resistor after the power regulator but before the power decoupling cap so hopefully the cap will help out filtering any noise that is cause by the precision resistor.
Actually putting the resistor before the PCI board power regulator would make sense since you want to measure the total power dissipation of the board which would include the power regulator and the board.
Anyway, my 2cents.