like with any partition, you have to mount it.
if it's a FAT partition, it should work by default.
if it's NTFS, you need to have the ntfs kernel module, which may or may not be the case.
try mounting and see if it works.
p.s.
mounting is done like so:
where /dev/hdXY is the partition in question (XY will vary), and /mnt/win is a directory where you want it mounted (can be any directory, must be created first).
you can find out exactly which XY in /dev/hdXY you need to use by using fdisk.
assuming the partition is on the first hard drive, run
then type p to print the list of partitions, note which one is the windows one, then type q to quit. it will be something like hda1 or some other number.
if it's not on the first hard drive, then try /dev/hdb, /dev/hdc, /dev/hdd with fdisk.