Hey fellas,
I am not a mac pro here, so my question might look simple to most of you. on the mac, i can't copy(click>drag) files to my external, it says "the item can not be moved because my hard disk can not be modified" if i go to my hardisk info, under ownership&permission it says YOU CAN ONLY READ.
My Q is, how can i modify this in order to copy stuff to my external, or just use it to render FCP files onto.
Thanks!

In the finder, click on the external drive to highlight it, then go to File > Get Info. This will open the window which it sounds like you have already seen. At the bottom of that window under Ownership and Permissions, click on the triangle next to Details.

That will show you the name of the account which owns the disk, and the access priveleges for the owner and other users. Does it show your name as the owner? If not then you need to login to your computer with the owner's account in order to have administrative priveleges to change the read and write access. If it does show your name as owner, then you can change access to read and write if it isn't already so.