Beside your IDE cable (wide cable that plugs into the MOBO)and power connector , when looking at the back of the drive. See that connector with a little jumper. This is usually set to MAster. Take the jumper and set it to SLave (only if both HDD are connected on the same IDE cable/channel.
There should be a label above your connector which tells you how to set the jumper for different configuration.
Your manual should help you too or the manufaturer's site or if you post some specs, we might be able to help you more.
My gaming machine:
P4 2.8 GHz
2 X 512 MHz PC3200 in dual DDR mode
Intel D865PERL MOBO
integrated 6.1 MAX audio
Logitech duo MX mouse and KB
ATI RADEON 9800 PRO