So the 80GB is in as master right?
Set the jumper on the 40GB to slave and conenct the power and PATA cable. The BIOS should detect the drive automatically. If it is not formatted already you can initialize/format it in windows by right clicking on my computer->manage. Under the storage tree click disk management. You'll see the drive there, you can create partitions, format and what-not by right clicking on it.