If I may assume, that the HD and CD-ROM are the only devices that will be attached, then I'd have the HD on the Primary IDE controller, set as Master...and the CD-ROM setup on the Secondary IDE controller as a Master as well.....on the HD and CD-ROM there should be a label that will show you how to set jumpers, to set each device as Master/Slave.
Might as well point out, I'm assummin again, that you have the proper ATA100/133 IDE cable for your HD, make sure the blue end of cable plugs in to the mobo. On the IDE cable, it won't matter where your devices plug into, as long as jumpers are set on the devices.
Your motherboard manual, should help explain, most of this....if you don't have a manual, check out ASUS's website, you could maybe download one, if need be.