I ran into a problem recently where I wanted to copy some files from my Mac to an external hard drive to take to an office. Unfortunately the hard drive was formatted NTFS which Mac OS X cannot natively write to. I went to Paragon Software’s web site and downloaded a trial version of their product NTFS for Mac OS X. The trial was good for 10 days and since I did not know if I would need it again, I just used the trial version.
I downloaded and installed the software without issue. A reboot was required to finish the installation. After restarting, my external hard drive contents were available and I could drag files from the Mac and copy them to the drive normally. I was able to copy the files from the drive to a PC and they worked just fine.
NTFS for Mac OS X is only $19.95, so if you need this capability on your Mac a lot it is a pretty good deal. Paragon Software makes many other fine products so check out their site if you have other cross platform and native storage, backup, and partition needs.