uC measure voltage/current?

I've got a PIC16F877A in a project of mine and want to be able to measure 
the power usage of a device that it's driving. I thought that since the 877 
has a few ADC's I could use them to sample the Voltage and Current.

Has any one done this before and could offer some pointers or ideas? 

The Voltage can be from 0-12v PWM and the current can be up to 15 Amps.


Thanks

DaveC