Read-only support for NTFS has existed in the Linux kernel for quite some time now, and at this point it's a pretty mature driver. Write access to NTFS is something a little bit newer, and is usually provided in the form of the ntfs-3g driver. This is a newer driver and more prone to bugs, so be careful when working with any highly critical data. That said, I haven't had any problems with it, nor have I heard too many problems reported with it.
The official download location for ntfs-3g is http://www.ntfs-3g.org/
, although your distro's package manager probably provides a package for it. Once it's installed, you can mount an ntfs-3g volume at the command line like:
mount -t ntfs-3g /dev/sda /mnt/mountpoint
replacing devices and directories with their respective locations. Alternatively, you can do it through a GUI using your distro's provided tools.
Hope that made sense.