Unplug the 80Gb drive the first time you boot, just to make sure that you CAN boot it to windows ok. If this passes, make sure that the 40Gb drive is on the end of the IDE cable, and set the jumper switch near the cable plug to master or cable select. the first two pictures on
THIS site will give an idea of where this jumper is.
Connect the 80 Gb drive to the middle of the IDE cable, setting its jumper to slave or cable select.