External hard drive permissions

Hello all,

I'm fairly new to the Mac world, so please go easy on me. I've been having trouble with an external hard drive I've been sharing between a PC and Mac.

I bought a 1TB Western Digital external hard drive a while back and I partitioned the drive into 2 portions - one that was formatted NTFS and one that was formatted Mac OS Extended (Journaled). I have MacDrive on my PC, which runs Windows 7, so I can read/write on both formats.

The problem arose when a few days ago I found I couldn't write to the Mac formatted portion of the hard drive from my Mac Book Pro. I can still access and write to both portions when I use my PC, so I figure it's something that happened or changed on the Mac. I've searched around a little for help on this problem, but the majority of answers seem to be with changing the permission on the hard drive. The thing is, when I use "Get Info" on the Mac formatted portion, I can't change the permissions (they're all greyed out and unclickable). I'm stumped as I've exhausted my knowledge of the workings of the Mac machine.

Is there anything I can do to fix this?

For reference, my Mac Book Pro is running Mac OS X 10.5.8.