Shouldn't cause you too much trouble to do this if you are planning to install NT, 2K or XP (not 98 or Me). When you run setup, just choose the option to install a new copy (not upgrade). During windows setup you should be able to change the install location for windows files to the d: drive. Windows setup should detect that you already have an OS installed and add the newly installed version as a second option in the boot.ini file. You can choose which version you want to go into when you first boot up.