trouble transferring files?

First off hi all, I just bought a 13" macbook pro and I love it. But I am new to mac and having trouble. I put all my movies and music on an external hard drive to save space on my computer. Then as I get new stuff I stick it on, no problem on my pc but on my mac not so much. I can pull files off my portable hard drive no problem but my mac will not let me put anything on. What gives? Any help would be great. Thanks.

What is the external drive formatted as? Right click the drive > Get Info > Format. I am going to assume it is formatted as NTFS which by default will be mounted read only. Try this app to mount it read/write (haven't tried it myself but it is frequently recommended) if it is indeed an NTFS formatted drive.

Thanks for the quick reply worked like a charm

For future use you should really reformat that drive for Mac. Of course you'll need to back up your stuff first, but you're doing that already of course.