Sorry, I just read your previous post. If you bought a completely seperate drive just for whatever brand of *nix you get, just connect it physically the same way you would any other drive.

As far as setup, install the intended OS on your second drive and setup the boot manager provided (ie. LILO, LOADLIN, GRUB, etc) to dual boot your system... I'm guessing you have some brand of Windows installed on your primary drive.

Please post back if you have more questions.