Greetings,
Can you please provide more information, as to what method you used to install FreeBSD onto your system, and what choices you made during the install? While I do know how to make a multi-boot install with FreeBSD. The directions, and/or corrections, depend on the approach that was taken. For example; you should have been presented with the option to install to the MBR, and to have been given the option to use a loader menu, when FreeBSD discovered you had other operating systems on the disk(s).
--chris