|Depending on the motherboard you may not need to worry about which to install first or using a boot loader, which can cause problems if one of the OSes or drive has problems.|
My system has three hard drives. Two IDE and one SATA.
When first booting the system if I tap F11 I then get a menus to select what to boot from. ALL drives, including the optical drives are listed. You simply highlight the drive you want the hit enter.
The advantage of this setup is that the hard drives are totally independent of one another, so removing or adding a drive has no impact on the others.
Look at your manual to see if you have those BIOS options available.
If so, you just perform custom/advanced installs and choose the hard drive you want to use for each OS.
Doesn't matter if both IDE hard drives are on the same IDE controller channel if you are not going to use the other drive for programs or storage while in the either OS. You may only have one IDE controller anyway.
You can still partition the drives if you want. If you install a second OS on either of the drives then you will get the normal Windows boot loader after selecting the hard drive.
When using the above system the normal boot order (default) will prevail and if you don't tap F11 you will boot to the first hard drive in the list.