I would suggest installing whatever distribution you like on the 300 Gb drive.
Install and configure samba, get the box up and running on your network.
Create a /nt folder in /usr
cd /usr
mkdir nt
Next, shut down and install one of the other drives, and reboot.
Watch the boot on the monitor, and you'll see the second drive get probed. it will show up as ad1 or ad2. make a note of that for the next step.
Let's say it probed as ad1.
mount that drive on the filesytem like this:
mount_ntfs /dev/ad1 /usr/nt
If that goes OK, then
cd /usr/nt
ls
<there is your stuff>
Now you can copy the contents out of there into the 300GB drive.
man cp for the details of that.
after you get the hang of that, you can reformat the emptied drive to suit the distro or unix of your choice, and permanently mount the drive using /etc/fstab or wherever your distro does it.
Because of the way filesystems are mounted, there are no drive letters.
For example, if one of those 250's were to be for foreign films, you could
mkdir foreign_films
and mount it there.