You should be able to access it. Try to mount it with the "ntfs" option as the used file system (or "vfat" if it is an old FAT32 Windows partition). To get read and write access you need the ntfs-3g package.
Example: If you have a sda1 partition with NTFS and a mount point "/mnt/i-want-my-data" you can try to mount it in a terminal window:
Code:
mount -t ntfs /dev/sda1 /mnt/i-want-my-data
If this doesn't work out of the box you probably need to recompile your kernel with ntfs enabled. I bet there is some info in the really helpful Debian user guides/handbook.