One useful but undocumented (and presumably unsupported) feature of Snow Leopard is the ability to mount NTFS volumes in read/write mode. The simplest way to do so seems to be as follows:

Get the UUID (Universal Unique Identifier) for the volume you wish to mount with write support — Disk Utility’s ‘Get Info’ command should provide the requisite information.

Open or create /dev/fstab with a text editor and add the following line, substituting the UUID from (1).

UUID=<REPLACE-WITH-DISK-UUID> none ntfs rw

Remount the volume or reboot. You should also be able to mount a volume in the same manner with a terminal command:

$ mount_ntfs -o rw [device] [mountpoint]

In my brief use of this feature I haven’t encountered any trouble, but please be protective of your data and don’t try this with anything you can’t afford to lose. Nonetheless, this route has real advantages: it’s faster than MacFuse + NTFS–3G, without the extra cost and 3rd-party kernel extension of Paragon NTFS.