I have a Mac Book Pro. When I attach my external hard drive to it, I can only read rights. How to I get read and write rights?
A common cause of this would be the external drive being formatted in NTFS.
If your external hard drive is NTFS formatted (a common Windows format), MacOS X can only mount it read-only. There are third-party add-ons that would allow a Mac to write to a NTFS, but out of the box, Macs can read but not write to this format.