Home to the NTFS filesystem driver for OS X.

25€ — "Tuxera NTFS for Mac delivers the fastest NTFS data transfer speeds you can have on Mac while protecting your data with its new, smart caching layer."

"A simple utility designed to mount NTFS volumes in read/write mode. Although not officially supported, Snow Leopard is now able to mount NTFS volumes with both read and write support. NTFS Mounter simply uses this ability, and provides a simple user interface to the mount command for NTFS volumes."

I booted into Bootcamp (holding down the Option key when starting up my iMac), and ran the following command: CONVERT C: /FS:NTFS and selected the option to have it run the conversion at next startup. After booting back into Windows, the conversion was done in less than 5 minutes.