With my Mac, I can "read", but not write, to my new 1TB hard drive. With Windows, I've of course got no problems with it.
It looks like your drive was format as NTFS. Macs can read but not write to NTFS formatted drive. If you albsolutely want to keep your drive as a NTFS drive, you can install NTFS-3G (free). You can read more about NTFS-3G at the following address: http://macntfs-3g.blogspot.com/