I had a similar experience myself when I hooked up my new 2TB external drive to my Mac Mini server, so I can show you how I fixed the problem. In particular, it doesn’t natively support computer drives that are formatted as NTFS, the Windows NT File System, a very efficient file system designed for Windows computers that supports extremely large file sizes.
While the majority of the time you should be able to just plug in any sort of external hard disk or drive, sometimes Mac OS X does get a bit picky about write permissions based on how the drive is initially formatted.
