Putting both Windows and *nix on a system is simple.

Now I'm speaking out of Linux experience, but since Linux is based of Unix, it should be the same...

First thing is to install Windows.
Then install a partitioning tool (ie: PowerQuest Partition Magic)
Then partition off your drive (1 Pri Part for Win (either Fat32 or NTFS), 1 Pri Part for Unix (Unix fat)
Then install a bootloader (ie: LILO or Grub from Linux, Bootmanager for Win)
Then install Unix on the second partition.
Then modify the bootloader to recognise both OSs and determine which is the main loader
(ie: which OS boots first)

That should be it, in it's simplest form.