firstly do you want both hard drives. I personnaly would just use the new one now.
On the back of your hard drive are jumpers. Make sure that the new one is set to master and connect on the end cable. Make sure that the red wire on the ide cable is nearest the power cable. The set the second hard drive to slave and connect it to the middle connector on the ide cable. This may slow performance as you are mixing very old with new.
From here make sure that in the bios (hold delete or a key which will be shown in print on the boot up screen) that the hard drive with the operating system is set to boot up first. It will be in one of the first options on the bios screen.
I would just use the single new drive as master on the end. then install your o/s onto that.