If it is NT 4.0 then you cannot install the OS to a partition larger than 4GB without using some tricks. Windows 2000 and above will allow you to install on any partition size. Depending on version and system configuration you may need to use newer drivers at install time than are available with the NT install software. To do this you need the driver disk and you hit F6 during the initial black screen with the detecting hardware message. You will be prompted during the blue screen portion of the install for the driver disk.