Always install Windows first and let Linux clean up it's mess.
I think you misunderstood. Windows install: partition X GB for NTFS and Windows boot partition. THEN Linux install: partition Y GB for ext4 & swap. THEN: wanted to take the unpartitioned space (~80GB) and format that to NTFS using Linux. Linux didn't even see the damn unpartitioned space, and once I got it to do
that, it didn't let me write to the partition table no matter what I did. Windows let me write to the table... and also decided to overwrite my Slackware partition. Win.