Question...

Hey everyone. I just got an external hard drive that I'm hoping to use between several computers. It shows up just fine on my Linux box (Ubuntu Breezy Badger) and I can access files, but I can't write to it. I'm told it's on a read-only disk, and I can't simply change permissions. On my Windows XP box, I can write to it just fine. Any advice or suggestions on how I can get my Linux box to write to this hard drive? I'm new to Linux and still trying to figure everything out. Thanks!