Most BIOSes will give you some options which will end up doing what you want. When I said "Most", that excludes the BIOSes from a lot of prebuilt machines such as HP, Compaq, Dell, eMachines and such. Some of those will provide the settings I mention and some won't.
If your machine has a decent BIOS you can do either one of the following:
1. In the screen that lists your IDE drives, you can manually set each drive to "none" or "disabled" (instead of "auto") - This is very often in the opening screen. It is also sometimes found by selecting "hard drive detection" or something similar to that.
2. In the "advanced options" (if your BIOS provides them) you can disable the primary and secondary IDE controllers. This will most definitely result in your machine not attempting to detect IDE drives.
In either case, it is very important that you enable "Boot from other devices" or "Boot from SCSI" (depending on your BIOS verbage) under the BOOT ORDER menu (which your BIOS hopefully provides).
If you don't see any of the options I mentioned then you might actually be out of luck.
HTH.