By default with MAC OS X you are able to mount a NTFS formated hard disk only with READ priviledges. But what if you have an external HD with NTFS format and you want to transfer files TO it? Then you need NTFS-3G for MAC.
DOWNLOAD http://rapidshare.com/files/179522025/NTFS-Read_Write-MAC-OS-X.zip and install MacFuse and NTFS-3G (FIRST RUN THE MACFUSE PACKAGE !!) and after a (short –since you are on a MAC and not WindOS-) reboot , your leopard will mount all NTFS disks with READ/WRITE capabilities.