As long as Apple doesn’t activate the NTFS driver that is supposed to be hidden in Snow Leopard, here is a quick way to format a drive (say, an external usb drive) to NTFS.
1/ Install the free MacFuse, which is a base for installing additional third party file systems on the mac
2/ Install the free open source driver NTFS-3G written by Tuxera (if you need this mucho times, you might want to think about buying the commercial driver which is more advanced, is only 25€ and comes with a lifelong upgrade). Otherwise the open-source driver works just fine.
3/ In the Mac’s Disk Utility, choose the drive and format it to NTFS-3G (an option which is only shown after installing the above).
4/ Done !