I did install Fedora 18 on a machine using Windows XP.
To do so I first modified the original only partition used totally by Windows and created partitions for Fedora 18 using GParted ( http://gparted.sourceforge.net/download.php )
From almost 100 GB I left only 32 for Windows (/dev/sda1, ntfs) and made a separate 4 GB patrition for My Documents (/dev/sda2, ntfs). The rest for Fedora this way
/dev/sda3 ext4 /boot 256 MB
/dev/sda5 swap swap 2 GB
/dev/sda6 ext4 / 4 GB
/dev/sda7 ext4 /usr 16 GB
/dev/sda8 ext4 /usr/local 4 GB
/dev/sda9 ext4 /var 3 GB
/dev/sda10 ext4 /tmp 1 GB
/dev/sda11 ext4 /home 40 GB
After that I started Fedora 18 installation from a DVD.
* In the main menu I selected Keyboard layout, software to be included -all other options were selected by default
Then, in the partition area
+ selected the disk
+ selected the type of partition to standard
+ told Anaconda I wanted no help in doing the partition
+ then clicked on Claim free space button
Anaconda did recognize partition and showed this partition as Unknown, the ntfs included.
It recognized the labels as I had defined them in GParted.
Then it was only matter of setting mount points with the exact names as the labels.
And check in Reformat box.
I didn't cypher data so not to mess around.
As I clicked on Apply changes button, the partition was moved in the left box to the New Fedora Installation area at the top.
It automatically separated data partitions (/usr/local and /home) from system partitions.
Checking the Finish partitioning button brought me back to main menu and Fedora 18 installation run seamlessly.