Hard Drive won't mount in OS X 10.5

Hard Drive won't mount in OS X 10.5

So I have an internal 500GB Western Digital HDD, and it's formatted at NTFS, but it won't mount in OS X. Both Windows and Ubuntu Linux can read and write to it perfectly fine, but OS X says the file system is unreadable. I have used this hard drive before with OS X and it worked flawlessly, but now when I boot I get a "OS X cannot read this filesystem" error.