Sounds like the drive is formatted as NTFS, which OS X only has read-only support for by default. So you can either buy a third party program to add this support, format the drive as FAT32, or take your chances with ntfs-3g.
Hey guys, I just needed some urgent help.
My friend wanted some files to be transferred to his external hard drive from my Mac. As he is a Windows user, I guess his hard drive is formatted for Windows as well. As I plug in the hard disk in my Mac, I can't transfer the files. It says something like "the disk cannot be modified".
So, please help me on how can I transfer this files from my Mac and if I do format it to work with the Mac, will it work for Windows later?