I'm running CentOS 6.3 on a dual-boot machine with Windows7. In the Windows side, I created an NTFS partition on an SSD and it works well from there. When I boot into Linux and try to mount that partition, it complains that I must specify the filesystem type.

If I run fdisk on it: it complains: WARNING: GPT (GUID Partition Table) detected on /dev/sda. The util fdisk doesn't support GPT. Use GNU Parted. fdisk displays that partition as having Id=ee, and System=GPT.

If I run 'blkid' on the partition, it returns nothing.

In Linux, how can I mount this partition?

use mount command like this :

don't forget to run mount with root access if needed
you can use gfdisk instead of fdisk to have GUID support as fdisk says you can also use parted which have support for both mbr and guid .
did you run blkid command with root access ? because when you run it without root access it gives no output .

If you want to write to it from CentOS you'll need the ntfs-3g package from EPEL. I'd be guessing the in-kernel support isn't enabled in RHEL/CentOS, so you'll need ntfs-3g regardless. Plenty of articles online.