I just installed Fedora 18 onto my housemate's laptop (at her request). I downloaded a Live CD image, wrote it to a USB disk (using livecd-to-usb-disk), and booted from there. I had to choose an EFI boot loader for the image, or it just sat with a blinking cursor. That's fine, though.
When I went to install it to the hard disk, it announced that up to 87GB could be reclaimed from the hard drive for use by Linux but then proceeded to not give me any options to do so other than deleting existing partitions. I don't want to lose existing data, I want to preserve it. I wanted to shrink the existing ones. Googling a little brought about references from others about resizing, and I was not sure why I did not have a "shrink" option.
Ultimately, I had to do it manually (which is a large usability failure). I used ntfsresize, following its instructions to do a test run first, and then ran it for real. It had to relocate a fair amount of data. It seemed to work (and it did). It gave me some vague instructions on how to resize the partition (using fdisk). I had a look at cfdisk, which didn't seem to let me specify the starting sector if I deleted and replace the existing NTFS partition, so I used fdisk itself. (I haven't had to do that in a while.) The trickiest part was calculating the correct size to make the replacement partition because ntfsresize worked in with SI decimal prefixes (e.g. where 280GB = 280*1000*1000*1000 bytes), and fdisk works with IEC binary prefixes (e.g. 280GiB = 280*1024*1024*1024 bytes). The difference is ultimately substantial. Fortunately, I converted the number of bytes ntfsrezise reported into sectors and just set it using those.
I let chkdsk run from Windows and the file system checked out and I was able to boot it successfully. (Everything is backed up in case something has gone wrong). Then I ran the anaconda installer from the F18 live USB disk, and this time it automatically detected the newly freed space (only 20GB) and the installer worked smoothly from there on out. Very smoothly, in fact. :)