It all depends on how you installed Windows 7 as to where your Master Boot Record is (MBR).
If you installed Windows 7 on to the 4th partition of your SATA disk whilst booting from your IDE then I would imagine when you boot up you get a choice of operating systems. However no MBR will exist on the SATA disk because it used the primary partion on your IDE when you installed it.
If however you booted up with your SATA as your primary disk and installed Windows 7 then an MBR will exist on the SATA disk so the bios switch will work.
If you did the first way, you may want to trash your windows 7 setup and go the bios route and re-install so you get an MBR and then you can use the bios for deciding which one to boot into - most modern bios have the facility to allow a pompt and boot to select boot device so may be easier to turn that on. You may be lucky and be able to do an upgrade/fix on the existing installation but usually those are not available in the beta products.